Recommendations for Main Scope for DSO Imaging w/ Sony A7III or Canon 1100d

Hi Nick,

I guess your questions all depend on your preferred targets. The 135/2 as well as the WO ZenithStar 61 (although I do not own it) are really widefield scopes/lenses. Especially with large sensors, they are able to capture a huge part of the sky. The ZenithStar is with 360mm focal length about 3 times longer, but is is still widefield compared to other scopes. The 135/2 is much faster, but personally I would go with the WO. But there is another thing to keep in mind…

I also do not know the star adverturer. But it can handle 5kg as said by the paper. The WO is about 2,2 kg. With the camera, the guide scope and the guider you will be very close to the limit. In my experience, you will be on the edge of what is possible. I do not say it can't work, but you pay a lot of money for a bigger scope on a small mount and you take the risk it won't work. For me, the 135mm is the better choice here. But maybe someone else has a different point of view.

Wide angle scopes/lenses are a great choice for nebulae and bigger portions of the sky. The images can be really great and personally I love them. However, if you want to go for galaxies, you will not come very far. Maybe M31 is an exception on the WO, but even the larger galaxies will appear only small in your images.

I totally understand you point of view. I experienced all of this myself. Many of us did. But for me, the most important thing in astro photography is the mount. With a good mount, you can get much better images. A DSLR and a simple (tele) lens will do the job in the beginning. Your images are much worse, if you own a good lens or scope on a weak mount.

Talking about dedicated astro cameras, they may be the next step. Your Sony or your Canon will help you to get started. While learning the basics, you will have time to think about pixel size, focal length, over-/undersampling and other important parameters of the sensors.

I know, that you will go your own way and I'm sure, you do the things that are already in your head in one way or another. But I lost a lot of money while buying so much things I don't use anymore. If I would start again, I would buy a really good mount, then a medium scope and then all the other stuff that is needed.

I hope you find your way and that you keep your interest in AP alive. So clear skies to you…

Christian

Christian Großmann:
Hi Nick,

I guess your questions all depend on your preferred targets. The 135/2 as well as the WO ZenithStar 61 (although I do not own it) are really widefield scopes/lenses. Especially with large sensors, they are able to capture a huge part of the sky. The ZenithStar is with 360mm focal length about 3 times longer, but is is still widefield compared to other scopes. The 135/2 is much faster, but personally I would go with the WO. But there is another thing to keep in mind...

I also do not know the star adverturer. But it can handle 5kg as said by the paper. The WO is about 2,2 kg. With the camera, the guide scope and the guider you will be very close to the limit. In my experience, you will be on the edge of what is possible. I do not say it can't work, but you pay a lot of money for a bigger scope on a small mount and you take the risk it won't work. For me, the 135mm is the better choice here. But maybe someone else has a different point of view.

Wide angle scopes/lenses are a great choice for nebulae and bigger portions of the sky. The images can be really great and personally I love them. However, if you want to go for galaxies, you will not come very far. Maybe M31 is an exception on the WO, but even the larger galaxies will appear only small in your images.

I totally understand you point of view. I experienced all of this myself. Many of us did. But for me, the most important thing in astro photography is the mount. With a good mount, you can get much better images. A DSLR and a simple (tele) lens will do the job in the beginning. Your images are much worse, if you own a good lens or scope on a weak mount.

Talking about dedicated astro cameras, they may be the next step. Your Sony or your Canon will help you to get started. While learning the basics, you will have time to think about pixel size, focal length, over-/undersampling and other important parameters of the sensors.

I know, that you will go your own way and I'm sure, you do the things that are already in your head in one way or another. But I lost a lot of money while buying so much things I don't use anymore. If I would start again, I would buy a really good mount, then a medium scope and then all the other stuff that is needed.

I hope you find your way and that you keep your interest in AP alive. So clear skies to you...

Christian

Christian, thank you for such a lovely reply and sharing your thoughts!

My SA is only 6 months old so I won't be able to buy another one anytime sooner. But I get your point. After buying it, I thought the same thing that I could have spent a little more on a GoTo or a better mount but as I was starting off and didn't have much idea about tracking I though I would start with this one.

From what I read, WO Z61 is 1.45 kgs but after attaching the Field Flattener and T-ring it might be closer to 2Kgs (not sure how much those things weigh).

The reason I am getting confused is because the Samyang 135 f2 is not cheaper here and if I add around 300 USD to my budget, I can get WO Z61 with all the attachments etc. so if I go with WO option would I have anything to loose except the money...lol?

But I guess, I need to check how many people are successfully using WO Z61 with their SA and make a decision accordingly, if that's the only major thing I need to worry about?

Clear skies to you as well and thank you again for your insights. Much appreciated

Regards,
Nick

I don't know much about the Samyang, except that it is often mentioned in Astro blogs. It seems to be a good choice. But it is a photo lens and although it is a prime and may be of high quality, there are usually some downsides to photographic lenses. They contain a lot of glass in several groups to correct for some errors of the different wavelengths of light. But that means, that there are more glass surfaces that can reflect light and create flares. Then the lens has to focus from about a meter to infinity, which usually is done by compromising some properties. The third and maybe most important thing is the focus ring. With an aperture of 2.0 you have to get the focus really right especially with larger sensors. That may not be a huge problem in the 135mm range, but I think chances for errors are good here.

The WO on the other hand is made for astro imaging. It has a fine focus with 1:10 ratio. It is much easier to make small adjustments here. There are less lenses, because the scope must not reach near focus. So it is made to focus at infinity. The image quality, especially in the corners, should be much better, I guess. I used to use a 300mm f/4 L USM lens on a Canon 5D Mark II for my first images and even a cheaper scope can easily handle the image quality in the corners better than this expensive prime lens. The WO is not a cheap scope and WO is known for their image quality. So I guess here are some advantages.

That is, why I would definitely choose the WO. I guess @John Noble has similar thoughts, when he was mentioning he would also choose it.

CS

Christian

John Noble:

John, thank you for sharing your thoughts! Much appreciated

I think iOptron has a similar weight limit as SA (i.e. 5 Kgs) or is it different? If it's the same, is mounting Z61 on a DSLR with Guide Scope and Camera would be within the limits and is balancing the setup not a problem if I go for Z61? Any insights into that would be much helpful.

As I am fairly a beginner, not sure if I understand about the image scaling you mentioned above. Can you elaborate on that a bit please?

Regards,
Nick

Nick,

Firstly I'm not the right guy to get into too many details on this, there are others out there with plenty of opinions and detailed understanding of the math!

The image scale is the amount of sky per pixel. To keep it really simple you want your image scale to be half the seeing conditions so you capture as much detail as possible. If the scale is too small you are oversampling the image if it's too big you are under sampling. Also the smaller your image scale the better your guiding needs to be.

I typically aim for an image scale between 1 and 2 arc seconds per pixel from my suburban back yard which matches typical seeing conditions and keeps the demands on my mount manageable. In reality for starting off an image scale ween 2 and 4 is going to be a big help as it will be much more forgiving and yet still yield good results.

There is a calculator on Astronomy Tool which helps you calculate image scale and CCD/Camera suitability - that's where I pulled the data for your set up. The Z61 is on the edge of undersampled and the 135 is really quite undersampled.

On the SkyGuider I found it good for 120 s guided exposures. The issues wasn't the weight it was more the DEC drift as you can't guide in DEC. Lets be clear if the bug catches you will be getting a new mount but your mount will get you through the initial learning curve. Here is a shot of M8/M20 region I took with the set up.

Hope that helps.

The main issue with undersampling is, that the small stars are looking like rectangular blocks, because the light from them is hitting only one or slightly more pixels. This is not very pleasant. When oversampling, the light of the stars is spread over several pixels and therefore is not as effective. Because of the seeing, the air is flirring and the light from the star is changing its position on the sensor slightly. There are more photons needed to expose all the pixels. So your exposure time increases very soon to get the same result as from a well matched pixel/focal lenth ratio. In the range between 1 and 2 arc seconds there is rarely a problem.

Christian Großmann:

John Noble:

John, thank you for sharing your thoughts! Much appreciated

I think iOptron has a similar weight limit as SA (i.e. 5 Kgs) or is it different? If it's the same, is mounting Z61 on a DSLR with Guide Scope and Camera would be within the limits and is balancing the setup not a problem if I go for Z61? Any insights into that would be much helpful.

As I am fairly a beginner, not sure if I understand about the image scaling you mentioned above. Can you elaborate on that a bit please?

Regards,
Nick

Nick,

Firstly I'm not the right guy to get into too many details on this, there are others out there with plenty of opinions and detailed understanding of the math!

The image scale is the amount of sky per pixel. To keep it really simple you want your image scale to be half the seeing conditions so you capture as much detail as possible. If the scale is too small you are oversampling the image if it's too big you are under sampling. Also the smaller your image scale the better your guiding needs to be.

I typically aim for an image scale between 1 and 2 arc seconds per pixel from my suburban back yard which matches typical seeing conditions and keeps the demands on my mount manageable. In reality for starting off an image scale ween 2 and 4 is going to be a big help as it will be much more forgiving and yet still yield good results.

There is a calculator on Astronomy Tool which helps you calculate image scale and CCD/Camera suitability - that's where I pulled the data for your set up. The Z61 is on the edge of undersampled and the 135 is really quite undersampled.

On the SkyGuider I found it good for 120 s guided exposures. The issues wasn't the weight it was more the DEC drift as you can't guide in DEC. Lets be clear if the bug catches you will be getting a new mount but your mount will get you through the initial learning curve. Here is a shot of M8/M20 region I took with the set up.

Hope that helps.

The main issue with undersampling is, that the small stars are looking like rectangular blocks, because the light from them is hitting only one or slightly more pixels. This is not very pleasant. When oversampling, the light of the stars is spread over several pixels and therefore is not as effective. Because of the seeing, the air is flirring and the light from the star is changing its position on the sensor slightly. There are more photons needed to expose all the pixels. So your exposure time increases very soon to get the same result as from a well matched pixel/focal lenth ratio. In the range between 1 and 2 arc seconds there is rarely a problem.

So from what I understand, the Z61 is at the edge of undersampling which makes it a less preferable option here? I don't want to spend on a scope which later during the process is found to be not so sharp or effective. The main purpose of spending on a scope is to get cleaner and sharper images and of course the FOV it provides. I am confused as to whether I should go with this one or there are better ones out there which can be mounted without crossin the maximum payload limit on the SA 2?

Dmitrijus Tiazlovas:
Couple things I can add from my experience choosing between a camera lens and a scope. Sorry if some of it is kind of obvious but maybe will be useful.

If you are looking for a camera lens for astro, make sure to check second hand market or people/companies lending photo gear. In Eu a used Samyang 135 f/2 goes for ~300. Personally I still haven't bought any lenses for wide field astro, since I can just borrow a $2000 piece of kit for like $30 per day. That being said, this only works out if you only rarely do wide field. Used telescopes are much harder to find but not impossible.

When it comes to quality of older Samyangs, sadly it can be a bit of a hit and miss. Generally corner sharpness is not really a priority for portrait camera lenses.

One more thing. If you get an f/2 lens, don't get used to such fast optics. It was a real shock moving back to f/4.8 or slower scope

Understood! Thank you for sharing your thoughts Dmitrijus, much appreciated!

Christian Großmann:

Christian Großmann:

John Noble:

John, thank you for sharing your thoughts! Much appreciated

I think iOptron has a similar weight limit as SA (i.e. 5 Kgs) or is it different? If it's the same, is mounting Z61 on a DSLR with Guide Scope and Camera would be within the limits and is balancing the setup not a problem if I go for Z61? Any insights into that would be much helpful.

As I am fairly a beginner, not sure if I understand about the image scaling you mentioned above. Can you elaborate on that a bit please?

Regards,
Nick

Nick,

Firstly I'm not the right guy to get into too many details on this, there are others out there with plenty of opinions and detailed understanding of the math!

The image scale is the amount of sky per pixel. To keep it really simple you want your image scale to be half the seeing conditions so you capture as much detail as possible. If the scale is too small you are oversampling the image if it's too big you are under sampling. Also the smaller your image scale the better your guiding needs to be.

I typically aim for an image scale between 1 and 2 arc seconds per pixel from my suburban back yard which matches typical seeing conditions and keeps the demands on my mount manageable. In reality for starting off an image scale ween 2 and 4 is going to be a big help as it will be much more forgiving and yet still yield good results.

There is a calculator on Astronomy Tool which helps you calculate image scale and CCD/Camera suitability - that's where I pulled the data for your set up. The Z61 is on the edge of undersampled and the 135 is really quite undersampled.

On the SkyGuider I found it good for 120 s guided exposures. The issues wasn't the weight it was more the DEC drift as you can't guide in DEC. Lets be clear if the bug catches you will be getting a new mount but your mount will get you through the initial learning curve. Here is a shot of M8/M20 region I took with the set up.

Hope that helps.

The main issue with undersampling is, that the small stars are looking like rectangular blocks, because the light from them is hitting only one or slightly more pixels. This is not very pleasant. When oversampling, the light of the stars is spread over several pixels and therefore is not as effective. Because of the seeing, the air is flirring and the light from the star is changing its position on the sensor slightly. There are more photons needed to expose all the pixels. So your exposure time increases very soon to get the same result as from a well matched pixel/focal lenth ratio. In the range between 1 and 2 arc seconds there is rarely a problem.

So from what I understand, the Z61 is at the edge of undersampling which makes it a less preferable option here? I don't want to spend on a scope which later during the process is found to be not so sharp or effective. The main purpose of spending on a scope is to get cleaner and sharper images and of course the FOV it provides. I am confused as to whether I should go with this one or there are better ones out there which can be mounted without crossin the maximum payload limit on the SA 2?

Using a DSLR or similar on a scope is slightly unusual, because the cameras are made for real life photography. As soon as you buy a dedicated astro camera, you will have another situation. In the lower prize segment, their pixels are usually smaller and you may even want to bin those pixels. Then the cards change a bit. Slightly undersampling is not a huge issue here. Take the 1 to 2 ratio as a suggestion. Using my ASI 183MM with 20 Megapixels and 2,4um pixels on my 8" Newton is oversampled a bit. I didn't thought about it until I learned about the relationship of pixel size and seeing. Now that I know,the images still look the same

Your cameras on a  Z61 is really a good starting point in my opinion. My 300mm lens on my 5D MarkII had nearly the same ratio and worked well.

Totally with you on the DSLR with Scope point you mentioned For now, I don't have a lens that would work well for DSO (I have Sigma 100-400 DG DN OS for Sony E but not sure if I can just stick to that and use it for DSO) so thought of getting Samyang but then the price here wasn't too cheap and comparing it with the price of the cheapest scope made me think that I should rather spend on a scope with my current setup. I think buying a good scope is as important as buying a dedicated astro camera so thought of taking some advice here. When you say, with astro camera there will be other issues when using this scope so I am guessing while buying a astro camera in the future I need to consider pixel size of the camera such that I am not oversampling or undersampling too much but there would be options available to me right? Not that, I will have to buy another scope to overcome that issue?

Totally with you on the DSLR with Scope point you mentioned For now, I don't have a lens that would work well for DSO (I have Sigma 100-400 DG DN OS for Sony E but not sure if I can just stick to that and use it for DSO) so thought of getting Samyang but then the price here wasn't too cheap and comparing it with the price of the cheapest scope made me think that I should rather spend on a scope with my current setup. I think buying a good scope is as important as buying a dedicated astro camera so thought of taking some advice here. When you say, with astro camera there will be other issues when using this scope so I am guessing while buying a astro camera in the future I need to consider pixel size of the camera such that I am not oversampling or undersampling too much but there would be options available to me right? Not that, I will have to buy another scope to overcome that issue?

I somehow think that you will buy another scope or camera. This is how it goes down in that rabbit hole called "Astro Photography" ... just kidding.

The Z61 is a good choice. This was mentioned several times here. There is no Do-It-All-Setup out there. It always depends on your likings. The Z61 and a smaller pixel astro cam is a good wide field setup. If you want to do galaxy work, we are talking about a completely different setup. Neither the scope nor the smaller pixel astro cam will really work with that. I didn't even mention the mount. So I do suggest as a starting point the Z61 with your cam and your star adventurer. Then you may think about buying the best mount you can afford. After this, you may think about a larger scope and choose one your mount can handle. Doing it in another order did work for some of us, but usually you may surely find the need to buy better and more expensive equipment, because something is not working as expected. The money you spent on the z61 is your least important problem then.

Starting with the Z61 will get you really nice images!!! While working with this setup you will get more experienced and things will clear up soon. Just be a little patient...

Got it! Just to clarify, the higher the FL the better the image sampling and I need worry less about it? So for WO ZenithStar 73mm ED APO Refractor the image sampling will be better than the 61mm? Sorry for all the questions I am throwing at you guys

Yes exactly but your mount will really struggle with the Z73 - that's exactly why I started with the Z61 and to be honest the difference is marginal in image scale. I have accumulated three refractors Z61, FLT 91 and FLT 132 - the image scale I get is roughly 2.1", 1.4" and 0.9" (all with ASI 2600 MM pixels) that covers just about every target I'm interested in. My point being the jump from the 61 to 73 isn't worth the added hassle of a new mount.

John

andrea tasselli:

Got it! Just to clarify, the higher the FL the better the image sampling and I need worry less about it? So for WO ZenithStar 73mm ED APO Refractor the image sampling will be better than the 61mm? Sorry for all the questions I am throwing at you guys

There is no better sampling, just a different image scale and different field of view (with the same camera). If I were in your shoes I wouldn't worry about image scale or sampling but how am I going to frame the target I wish and operate a mount with only RA motor. And, lest we forget, how I'm going to balance scope and camera (and possiby guiding scope and attendant camera) on a possibly flimsy tripod. Or, how about focusing the thing and operate the whole gizmo.? Those are the real world issues.

Andrea thank you for your inputs on this one as well I agree those are the real world issues which I would have to put all my efforts in the field but as I would be making a purchase for the scope in the near future I thought I would get an opinion on this.

Andrea thank you for your inputs on this one as well I agree those are the real world issues which I would have to put all my efforts in the field but as I would be making a purchase for the scope in the near future I thought I would get an opinion on this.

Those are the issues that would (strongly) affect your decision in matters of scope vs. lens otherwise I wouldn't mention them. A 135mm lens (not necessarily a Samyang) is easy to point to as well as balence on a ball-head. Doing that on the same setup with a scope of 360 mm of FL, well it isn't as easy I can assure you. In the UK the ZS 61 + flattener (which you would need) cost the same or less than the said Samyang (which is also of larger aperture).

Yeah, that's what made me think twice. I had been planning on buying Samyang but it was almost the same price as the Z61 scope.

For me, it would not be feasible to buy Samyang now and later buy some other lens/scope due to limited FL on Samyang and only restricted to few targets. Let's not count galaxies but would I be able to capture most of the nebuale and the Messier objects with Samyang?

I do have a Sigma 100-400 DG DN f/5-6.3 but I am not confident if that would yield good enough results or if it's well suited for this purpose. I just don't want to end up buying something just for the sake of it but something that I can use for a few years to get comfortable in this hobby and not restricted to just few or limited DSOs.

I hope you understand my dilemma here.

I appreciate your position and the conundrum you're facing. I'd probably first try my hand with your current lens and cameras to get a feel of what is like to shoot things you can't see and finding them in the dark. If the zoom lens you have (at 400mm)  allows you to do pretty much what you want to do but isn't performing as it should then you can go and grab a short focus refractor such as you're planning to do. Should it not then you must decided whether upgrade your mount or downsize your ambitions.

Incidentally, it doesn't seem your zoom is doing too shabbily according to this review:

https://www.the-digital-picture.com/Reviews/Sigma-100-400mm-f-5-6.3-DG-DN-OS-Contemporary-Lens.aspx