Advice on new scope

[Astro Noodles]

Hi Guys

I am planning to get a new scope and would like your opinions/suggestions.

I'm not going to pull the trigger on it just yet. Maybe October time if my willpower holds out.😓

I am after a small, lightweight, fast (less than f5), widefield refractor for astrophotography.

The Criteria I have set are as follows:

Must be able to achieve focus with a crop sensor DSLR.

Must be light enough to use on Ioptron Skyguider Pro.

Must cost under £1000 including all accessories required (flattener/t-ring/spacers etc).

So far, I have the field narrowed down to the following: WO Redcat 51, WO Zenithstar 61 II, Sharpstar 61 EDPH II.

Are there any others which I should be looking at? Are there any features about the three listed scopes which would make them a better choice than the other two?

Thanks

[Grant Fribbens]

I started out with the Zenithstar 61 but it is only a doublet but it does have FPL-53 glass and you can get a non-reducing as well as a reducing flattener which gives you two focal length options of 360mm or  288mm and I found it was really great starting out. For imaging a triplet or better is good so the Sharpstar 61 EDPH II is great but the only issue is you would have to use it with a flattener/reducer 0.8 for a focal length of 275mm and you may find the wide field of view an issue. The RedCat 51 has superb optics and would not need any flattener as it is of petzval construction with a flat field and had a focal length of 250mm. The ZS61 and 61 EDPH II are easier to add a focusing motor and may have a longer focal length than the RedCat 51 so it is all dependant on the targets that you want to go after.  HTH

[iapa]

 

Starwatcher Evoguide 50?

• 50mm Objective
• 242 mm (f/4.8) Focal Length
• 1.25" Fine Helical Focuser
• T2 thread / 1.25” Focuser Barrel for Camera / Eyepiece Connection
• Doublet ED lens with 2 Ohara glass lenses (1 lens S-FPL53
• Has a Matching flattener

I have an unopened Evoguide AND A Redcat 51 sitting. Would love to have had the SpaceCat available - purely on aesthetics.

Not had opportunity to use due weather but may have an hour’s sky tomorrow. Will see if I can compare them.

Edited May 17, 2021 by iapa

[Astro Noodles]

24 minutes ago, iapa said:

 

Starwatcher Evoguide 50?

• 50mm Objective
• 242 mm (f/4.8) Focal Length
• 1.25" Fine Helical Focuser
• T2 thread / 1.25” Focuser Barrel for Camera / Eyepiece Connection
• Doublet ED lens with 2 Ohara glass lenses (1 lens S-FPL53
• Has a Matching flattener

I have an unopened Evoguide AND r

Redcat 51 sitting. Would love to have had the SpaceCat available - purely on aesthetics.

Not had opportunity to use due weather

I thought that the issue with the Evoguide was that you couldn't achieve focus with a DSLR. 

I would be very interested to read you comparison between the two.

Edited May 17, 2021 by Astro Noodles

[Clarkey]

On 17/05/2021 at 18:14, Grant Fribbens said:

Sharpstar 61 EDPH II is great but the only issue is you would have to use it with a flattener/reducer 0.8 for a focal length of 275mm

I am looking at similar options and I have read some less than flattering reports about the Sharpstar - but I have no first hand experience. However, I guess this depends if you get a Friday afternoon model and also your expectations. I was seriously looking at the Askar FMA180 which has everything at a good price and appears to give pretty good results at F4.5. Also it is designed to take a T-ring. It depends on how 'wide' you want to do.

[Astro Noodles]

1 hour ago, Clarkey said:

I am looking at similar options and I have read some less than flattering reports about the Sharpstar - but I have no first hand experience. However, I guess this depends if you get a Friday afternoon model and also your expectations. I was seriously looking at the Askar FMA180 which has everything at a good price and appears to give pretty good results at F4.5. Also it is designed to take a T-ring. It depends on how 'wide' you want to do.

Hi Clarkey

Thanks for the suggestion. I don't know if the 40mm/180mm triplet f4.5 will offer me that much more than the camera lens that I'm using which is  57mm/200mm with 5 glass elements F3.5. Although I dare say that the quality is much better. And the price is attractive.

[The Lazy Astronomer]

On 17/05/2021 at 22:14, Astro Noodles said:

I thought that the issue with the Evoguide was that you couldn't achieve focus with a DSLR. 

I would be very interested to read you comparison between the two.

You are correct. For all but the tiniest of sensors (and I mean tiny!), you would need to use the flattener unless you don't mind severe field curvature, and the back focus on the flattener is only 17.5mm. There was some talk about a flattener from Starizona which had a larger backfocus, but don't know if that ever actually materialised.

[Clarkey]

1 hour ago, Astro Noodles said:

Thanks for the suggestion. I don't know if the 40mm/180mm triplet f4.5 will offer me that much more than the camera lens that I'm using

Yes you are right. Should have looked more closely at your signature.

I think the Redcat would be similar to your current set up at 250mm. I'm not sure how the Zenithstar doublet stands up in terms of colour correction. Another doublet option is the SW 72ED with a few upgrades - such as the focuser. I have an ED80 and have found it pretty good.

[AstroNebulee]

Such is the production and shipping of astro equipment at the moment, I'd order it as soon as possible then you may stand a chance of getting it by October 😊 I have the sw 72ed and love it and you can always get a flattener /reducer to make it even faster 

Edited May 20, 2021 by AstroNebulee

[Astro Noodles]

9 minutes ago, Clarkey said:

Yes you are right. Should have looked more closely at your signature.

I think the Redcat would be similar to your current set up at 250mm. I'm not sure how the Zenithstar doublet stands up in terms of colour correction. Another doublet option is the SW 72ED with a few upgrades - such as the focuser. I have an ED80 and have found it pretty good.

Hi Clarkey, I have had a play around with various scope/camera combos on a FOV calculator. The Redcat does offer a reduced FOV over the Tamron 200mm but it is not massive. I have the Redcat on the list because of its  proven quality and light weight. 

The ED72 is definitely an idea. I don't think it uses the same glass as the ED80 though, and would be towards the upper weight limit of my Skyguider  once I have added all of the other paraphernalia.

Edit: No-I'm wrong, The OTA is under 2kg so that would be OK. I shall add it to the list

Edited May 20, 2021 by Astro Noodles

[Astro Noodles]

27 minutes ago, AstroNebulee said:

Such is the production and shipping of astro equipment at the moment, I'd order it as soon as possible then you may stand a chance of getting it by October 😊 I have the sw 72ed and love it and you can always get a flattener /reducer to make it even faster 

FLO have 14 Zenithstar 61s in stock. Not much else though.

[Astro Noodles]

 

One of the things which worries me a bit is the greater precision required with a narrower FOV. I'm not ready to start guiding yet.

Edited May 20, 2021 by Astro Noodles

[Grant Fribbens]

I think the RedCat 51 with the SkyWatcher Star Adventurer Pro / iOptron SkyGuider is a great combination as it is light weight enough and has petzval design means that the field is nice and flat and the colours will be really good and at 250mm focal length will be easier to handle. With the ZWO F4 30mm guidescope and a ZWO 120mm Mini you can also do autoguiding easily. This is the setup that Peter Zelinka on YouTube has used for quite a while with very good results.

[iapa]

On 17/05/2021 at 22:14, Astro Noodles said:

I thought that the issue with the Evoguide was that you couldn't achieve focus with a DSLR. 

I would be very interested to read you comparison between the two.

Back focus is 20mm, but if you take the 40mm extension tube out it increases to 60.

So, I imagine that DSLR T2 adapter with a 5mm T2 extension would give you your 55mm. I think I have a 5mm somewhere I could try.

 

https://nightskypix.com/evoguide-50ed-review/

 

Edited May 25, 2021 by iapa
Rephrased last line for clarity

[Astro Noodles]

2 hours ago, iapa said:

Back focus is 20mm, but if you take the 40mm extension tube out it increases to 60.

So, I imagine that DSLR T2 adapter with a 5mm T2 extension would give you your 55mm. I think I have a 5mm somewhere I could try.

 

https://nightskypix.com/evoguide-50ed-review/

 

Hi Iapa. If it can be used with a DSLR, It's definitely worth considering at that price. I asked FLO and they said it can be done if the flattener is used.