My first setup, and I have question about H-Alpaha - Forums

Topic starter

Jan 10, 2024 · Edited: Jan 11, 2024

Thank you for granting me the opportunity to contribute to this forum. I am relatively new to this field and, truth be told, I have limited knowledge about DSOs. Nonetheless, my wife has been supportive, allowing me to accumulate a few tools for my endeavors. I am seeking advice regarding my camera and which filters would be compatible with my existing setup.

I own a standard Nikon Z7 and would prefer not to modify it. I initially purchased an H-alpha filter without fully understanding its functionality. Subsequently, I've been informed that on an unmodified camera, the H-alpha filter I have might be ineffective. It has been suggested that I would need to capture four times the usual number of frames to derive any significant benefit. I'd like to confirm if this information aligns with my setup below.

Given my focus on deep-sky objects (DSOs) and nebulae, I'm interested in acquiring two additional filters for my camera. As my birthday approaches, my wife plans to gift me these filters. I am seeking recommendations for filters that would complement my goals in astrophotography. Additionally, I would appreciate insights into any essential components or accessories that seem to be missing from my current setup, which could enhance its overall effectiveness.

1.Astromania Bahtinov Mask Focusing Mask for Telescopes - FM60mm for a Tube Outer Diameter (OD) from 65mm-100mm.
2.ZWO ASI120MM-MINI 1.2 MP CMOS Monochrome Astronomy Camera with USB 2.0# ASI120MM-MINISky Watcher 3.Sky-Watcher Star Adventurer GTI Mount Head Kit with Counterweight and CW bar - Full GoTo EQ Tracking Mount for Portable and Lightweight Astrophotography
4.Orion 8893 Field Flattener for Short Refractors
5.Sky Watcher Sky-Watcher EvoStar 72 APO Doublet Refractor – Compact and Portable Optical Tube for Affordable Astrophotography and Visual Astronomy (S11180)
6.SVBONY SV165 Mini Guide Scope

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andrea tasselli

Frequent contributor

Jan 11, 2024

The best present you can give yourself is a cooled astro-camera which would make a world of difference with your current arrangement. Having said that your best option in terms of filters are:

1. Good light pollution multi-band filter such as the Optolong L-Pro
2. A good narrow band filter such as the Optolong L-enHanced

Given that you have a full frame camera you'd need full frame clip-on filters which are not going to be cheap. In fact you could almost buy yourself a decent astro-camera for the same price but there you go.

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Dcolam

Jan 11, 2024

Hi Carl,

You are right, that the H-Alpha filter is not very efficient in a stock mirrorless camera such as yours. I would in general also inform yourself about color cameras and the different filters they have incorporated (bayer matrix, IR filter ect).
Having single line narrowband filters in front of color cameras is not as efficient as having for example a dual narrowband filter, which allows to capture two transmission lines at the same time (such as OIII in blue and green and Ha in red, usually). Those can work really well with modified mirrorless cameras (see my pictures taken with a modded RP). Or you go the astrodedicated route with a cooled camera such as the ASI533MC Pro or similar. In combination with a dual filter like the L-Extreme can result in very pleasant images (see again my examples together with the 72ED)

Drawback, you are dependent on a computer or ASIAir or similar to control your setup. The learning curve it steeper and you might end up getting frustrated.

IMHO, get yourself a cheap and used modified DSLR or dedicated astrocam in combination with a Dualband filter. Those are coming very cheap nowadays second hand. Together with the GTI, it will be much easier to just but everthing on top and start shooting. Do not bother with guiding yet. The 72ED is a good choice, I like mine a lot, but I am selling it rn because of change of setup.

Good luck, have fun and CS
David

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Jan Erik Vallestad

Jan 11, 2024

The RGGB bayer pattern on your camera is the reason why you would need 4x the exposure which holds true with every kind of OSC.

That being said I just want to add that there are loads of DSO's that you can go after with a stock camera. As a complete beginner I would advice against going on a shopping spree spending large amounts of money on specialized equipment until you've dabbed your feet into it first, and also got the hang of all the pre- and post-processing that you need to learn. You will pick up Ha signal with the Z7 (I have one as well) but it won't be able to capture it as efficiently and you won't get the faintest stuff.

That said plenty of nebula will be visible with a stock camera, also dark nebula, reflection nebula, planetary nebula, star clusters, comets etc. The faint ionized hydrogen/oxygen/sulfur stuff isn't everything that's out there.

As an example, I tested my Z7 with a 50mm lens on a simple tripod a bit last year and this is one of the images I got with only about 15 minutes:
https://www.astrobin.com/cm7ns9/

It's not a "wow" image by any means, and it's just a small short test, but it shows that a normal camera can be quite a bit better than you'd expect. I also have several other images that I took with my stock D800 and the older SWSA 2i a while back on my page, M31, M51 etc. So please feel free to check them out, AB has a lot of examples and a great way to see what's possible is to use the gear search function and look up the Z7 and possibly some of your lenses as well.

Adding the mount would be the absolute best and most important addition. The GTI is a great one and will carry the smaller scopes and most lenses without any issues.

If you want to add guiding etc then you would need a computer to control everything. Either a lap top or a mini PC/Asiair solution. As a first scope even the Evolux 62ED or one of the smaller Sharpstar/Askar options are great, the Sky Watcher line is very reasonably priced though, but if you have a set of lenses I would just start there. A 180mm or 300mm lens will get you a long way. There's a lot of large interesting areas out there to photograph with a wide field setup.

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andrea tasselli

Frequent contributor

Jan 11, 2024

he RGGB bayer pattern on your camera is the reason why you would need 4x the exposure which holds true with every kind of OSC.

This is very much untrue. The Bayer matrix or any other for that matter, has an effect in reducing the spatial sampling of an image but there is very little to distinguish it on a single pixel basis with a monochrome camera with RGB filters.

The real reason the OP has been advised to increase the exposure by 4x *when using the Ha filter* is that the stock cameras, by and large, have a sharp cut-off of the far red end of the visible spectrum and the amount of Ha light that IR/UV cut filters in a stock camera let pass through is about 1/4 of what otherwise would be if those filters were absent, which is why most of us using DSLRs for AP have them modified by removing said filter.

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Jan Erik Vallestad

Jan 11, 2024

andrea tasselli:
he RGGB bayer pattern on your camera is the reason why you would need 4x the exposure which holds true with every kind of OSC.

This is very much untrue. The Bayer matrix or any other for that matter, has an effect in reducing the spatial sampling of an image but there is very little to distinguish it on a single pixel basis with a monochrome camera with RGB filters.

The real reason the OP has been advised to increase the exposure by 4x *when using the Ha filter* is that the stock cameras, by and large, have a sharp cut-off of the far red end of the visible spectrum and the amount of Ha light that IR/UV cut filters in a stock camera let pass through is about 1/4 of what otherwise would be if those filters were absent, which is why most of us using DSLRs for AP have them modified by removing said filter.

You're quite right, my bad!

But as you're only collecting that specific wavelength with a OSC camera, using a NB Ha filter, most of the sensor won't be utilized due to the bayer filter array as only 25% of the pixels are collecting red. Wouldn't you agree? If so there's already a need for longer integrations. As you say, the UV/IR filter on a stock DSLR/Mirrorless would have vastly less sensitivty than say a 2600MC, from what I can tell the sensitivity on a Z7 is about 20% at 650nm vs about 80% on a 2600MC. Correct me if I'm wrong, but factoring this into the equation (depending on the wavelength of the filter itself) wouldn't you need substantially longer exposure time than just the three quarters?

As for RGB filters 100% of the pixels will always be collecting that specific light on a mono camera, whereas the OSC will spread the light onto the sensor through the pattern (25% R/B and 50%G). But you're probably right that it won't be that distinguishable with an equal comparison between the newer dedicated cameras. But RGB wasn't the topic, so we probably shouldn't digress.

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Brian Diaz

Jan 11, 2024

carl brown:
Thank you for granting me the opportunity to contribute to this forum. I am relatively new to this field and, truth be told, I have limited knowledge about DSOs. Nonetheless, my wife has been supportive, allowing me to accumulate a few tools for my endeavors. I am seeking advice regarding my camera and which filters would be compatible with my existing setup.

I own a standard Nikon Z7 and would prefer not to modify it. I initially purchased an H-alpha filter without fully understanding its functionality. Subsequently, I've been informed that on an unmodified camera, the H-alpha filter I have might be ineffective. It has been suggested that I would need to capture four times the usual number of frames to derive any significant benefit. I'd like to confirm if this information aligns with my setup below.

Given my focus on deep-sky objects (DSOs) and nebulae, I'm interested in acquiring two additional filters for my camera. As my birthday approaches, my wife plans to gift me these filters. I am seeking recommendations for filters that would complement my goals in astrophotography. Additionally, I would appreciate insights into any essential components or accessories that seem to be missing from my current setup, which could enhance its overall effectiveness.

1.Astromania Bahtinov Mask Focusing Mask for Telescopes - FM60mm for a Tube Outer Diameter (OD) from 65mm-100mm.
2.ZWO ASI120MM-MINI 1.2 MP CMOS Monochrome Astronomy Camera with USB 2.0# ASI120MM-MINISky Watcher 3.Sky-Watcher Star Adventurer GTI Mount Head Kit with Counterweight and CW bar - Full GoTo EQ Tracking Mount for Portable and Lightweight Astrophotography
4.Orion 8893 Field Flattener for Short Refractors
5.Sky Watcher Sky-Watcher EvoStar 72 APO Doublet Refractor – Compact and Portable Optical Tube for Affordable Astrophotography and Visual Astronomy (S11180)
6.SVBONY SV165 Mini Guide Scope

hi, what about you sky quality ( SQM ) or bortle , over bortle 7 , i recommend narrowband 3nm, or optolong ultimate or similar

andrea tasselli

Frequent contributor

Jan 11, 2024

But as you're only collecting that specific wavelength with a OSC camera, using a NB Ha filter, most of the sensor won't be utilized due to the bayer filter array as only 25% of the pixels are collecting red. Wouldn't you agree?

Not on a single pixel basis, it won't. And if you allow for some very nifty algorithm during debayering, the final image wouldn't be that much different from one taken with a monochrome camera and filters. I estimate that the net efficiency loss at around 10% in B and much less in G and R ( due to the organic dye being less transparent at shorter wavelengths than dichroic filters). Not also that some of the Ha light will be collected by both B and G photosites so even that argument isn't actually quite true.

Dcolam

Jan 12, 2024

andrea tasselli:
But as you're only collecting that specific wavelength with a OSC camera, using a NB Ha filter, most of the sensor won't be utilized due to the bayer filter array as only 25% of the pixels are collecting red. Wouldn't you agree?

Not on a single pixel basis, it won't. And if you allow for some very nifty algorithm during debayering, the final image wouldn't be that much different from one taken with a monochrome camera and filters. I estimate that the net efficiency loss at around 10% in B and much less in G and R ( due to the organic dye being less transparent at shorter wavelengths than dichroic filters). Not also that some of the Ha light will be collected by both B and G photosites so even that argument isn't actually quite true.

Yes exactly, I agree with Andrea here. I would like to perform a test at some point comparing my ASI533MC vs ASI2600MM cameras to really have an idea whether integration time matters. I assume not too much. Except maybe that with an OSC, one shoots through two filters (bayer matrix and any dual band filter), so the efficiency is worse. Not to mention, as Andrea stated, that the H-alpha will cross-over to the green channel, which is why sometimes it seems like the separation of structures (difference between OIII and Ha) is less pronounced in images taken with a dual NB filter.

However, there is a substantial difference in spatial detail between the two systems. And I do not think that this can be mitigated with more integration (correct me if I am wrong).

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andrea tasselli

Frequent contributor

Jan 12, 2024

However, there is a substantial difference in spatial detail between the two systems. And I do not think that this can be mitigated with more integration (correct me if I am wrong).

You can attain a similar spatial sampling (close enough on practical basis) with CFA drizzle but you pay a price in that SNR is halved thus you need twice as much integration to attain both goals, depth and sampling.

Jan Erik Vallestad

Jan 12, 2024

Aha, thanks for the information guys! It's an interesting topic. I've seen several videos on comparisons between OSC/Mono but I don't think I've come across something that really makes it apples to apples. I guess in the end it really depends on what you want to achieve/explore.

To OP: Sorry for derailing your post!

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