should I start with BRESSER REFLEKTOR 203/800 EXOS 2 GOTO - Forums

Topic starter

Sep 14, 2020

Hi everyone, I am pretty new in astrophotography. I would like ot buy Bresser Messier NT-203s / 800 EXOS-2 GOTO as my first telescope and mount for the purpose of astrophotography, as it fits into my budget. Do you think it is a good assembly to go with? I would use a Canon 450D.

Thanks in advance.
Regards,
Debarshi

Marius Bednar

Sep 14, 2020

Hi Debarshi

The 8" Newtonian is probably too heavy for that mount for astrophotgraphy purposes. Keep in mind that you will need to add a small guidescope (you can use the finder scope) or off-axis guider and a guide camera. Also the 800 mm focal length may be a little too much for that mount under that load. You would struggle to get round stars. While it is not impossible be aware that there is no margin left. For that class of mount I would use a 6" Newtonian; both the lower weight and the shorter focal length will make your entry into astrophotography less frustrating.

Also note that you will need a coma corrector or your stars towards the edges will not be pin-point.

Alternatively you could use an 80mm f/5-f/6 refractor, but depending on quality this might be priced above your suggested 8" nextonian. The shorter focal length makes a good match to your camera's pixel size and will be easier to handle (in terms of guiding to get round stars)

So to sum it up: I don't believe the 8" on that mount is the right choice to start into astrophotography.

Cheers
M. B.

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churmey

Sep 15, 2020

It's showing the assembly here on their site and at F3.9 it's obviously showing it for imaging:

https://www.bresser.de/en/Astronomy/Telescopes/BRESSER-Messier-NT-203s-800-EXOS-2-EQ5.html

In my experience you need about a 2/3'rds ratio. Imaging at no more than 2/3'rds weight of the mounts max payload capacity. Others might disagree, but in my experience, this is the threshold. Check your mounts max payload and check the total weight of your optical tube fully dressed out. If it's under 2/3rds of your mounts max payload, you should be ok for imaging.

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Debarshi Kumar Phukan

Topic starter

Sep 15, 2020 · Edited: Sep 15, 2020

Marius Bednar:
Hi DebarshiThe 8" Newtonian is probably too heavy for that mount for astrophotgraphy purposes. Keep in mind that you will need to add a small guidescope (you can use the finder scope) or off-axis guider and a guide camera. Also the 800 mm focal length may be a little too much for that mount under that load. You would struggle to get round stars. While it is not impossible be aware that there is no margin left. For that class of mount I would use a 6" Newtonian; both the lower weight and the shorter focal length will make your entry into astrophotography less frustrating.

Also note that you will need a coma corrector or your stars towards the edges will not be pin-point.

Alternatively you could use an 80mm f/5-f/6 refractor, but depending on quality this might be priced above your suggested 8" nextonian. The shorter focal length makes a good match to your camera's pixel size and will be easier to handle (in terms of guiding to get round stars)

So to sum it up: I don't believe the 8" on that mount is the right choice to start into astrophotography.

Cheers
M. B.

Hi Marius

Thanks for the quick reply. Honestly I have chosen EXOS2 because it is firstly cheap and secondly lightweight. But in order to reduce the weight of the total assembly, what if I buy one Skywatcher Apochromatic refractor AP 72/420 EvoStar 72 ED DS Pro OTA for astrophotography? It is lightweight (2kg), f/5.8 and nearly 400 euros at cost. I can use the Newtonian for observing, as it is pretty big (sometimes photography too, with not very large exposures). I have following options as well in my budget -

TS Optics Apochromatic refractor AP 70/420 ED V2 OTA
Tecnosky Apochromatic refractor AP 70/420 ED V2 OTA

Or should I go for Achromat tubes?

Regards,

Debarshi

dkamen

Sep 15, 2020 · Edited: Sep 15, 2020

Hi,

Achromats are for visual or guiding. They are not very good for astrophotography because only two colours focus the same.

The Evostar and the two refractors are very good for a beginner and of approximately the same caliber (actually TS Optics and Technosky are probably the same scope, differently branded). But no matter which you choose, you will also need a field flattener which adds another ~$200 to the cost. Or buy a dedicated astrocam with a smaller sensor which adds complexity and another $300-$500 while not necessarily being as good as your Canon.

See here for how images look without a flattener.
https://www.cloudynights.com/topic/637888-evostar-ed72-clear-aperture-without-field-flattener/

I am not saying this as a minus: all refractors need a flattener and all reflectors need a corrector, except in marginal use cases. Thing is, unless the flattener/ corrector is built into the telescope, that additional cost is never mentioned

I have very good experience from the TS Photoline 60/360 (and its associated flattener which I bought a week later), to the point that I am not thinking of getting a bigger refractor (I also have a catadioptric for larger magnification and if I go even further it will probably be a RC or a RASA). If I was starting today, I would probably go for the Evostar because:
-It has slightly larger aperture and smaller f-ratio, meaning it collects more light per pixel meaning shorter exposures meaning better.
-It includes a decent dovetail and a shoe for the guider scope, which I had to purchase separately for the TS.

On the other hand, the 60/360 is shorter and lighter, both advantages in my book.

Cheers,
Dimitris

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