Do we need a focal reducer for Skywatcher Evostar 72 ED Apo Refractor - Forums

Topic starter

Sep 25, 2020

Hi everyone,

I am thinking to buy one Skywatcher Evostar 72 ED Apo Refractor. Do think I should also buy the Skywatcher Field Flattener+ Focal Reducer (costs 230 euros) for it? Or should I only buy the OVL Field Flattenner (costs nearly 100 euro) for it, as the focal length of this refractor is already not that long (420mm nearly)? I would mainly like to use it for astrophotography. And basically should I need to spend 230 euros for a telescope of 350 euros?

Thanks and regards,
Debarshi

Jesco

Sep 25, 2020

Depends on what you want. The reducer changes the FOV and increases the speed of the scope. This can be nice.

If you don't need the faster speed and/or wider field-of-view, then go for the OVL flattener.

Some kind of flattener will be needed. Field curvature will be apparent without it.

Desire Astro

Sep 25, 2020

Depends on what you want. The reducer changes the FOV and increases the speed of the scope. This can be nice.If you don't need the faster speed and/or wider field-of-view, then go for the OVL flattener.

Some kind of flattener will be needed. Field curvature will be apparent without it.

what kind of speed of the scope?

dkamen

Sep 25, 2020

Hi,

A difference of 15% in effective f/ratio isn't so important, no matter how you look at it. Everything will be practically the same in terms of FOV, exposure times, resolution. So you basically want to look at their relative optical quality. I am reading very good reviewsabout the OVL flattener here, specifically from Evostar 72ED users:

https://www.firstlightoptics.com/reducersflatteners/ovl-field-flattener.html

it appears to work better than the dedicated SW flattener-reducer but suffer a bit in the threading department, something which you can fix with an extra thumbscrew fit adapter (which the SW flattener includes, btw).

I am a value for money person too. I agree with you that spending almost as much as the scope on the flattener seems a bit extreme, especially in this price range. Even if the SW flattener is better, is it 2.3 times better? I kind of doubt it

. If you ever buy a $230 flattener it will probably be for a bigger and more high end scope, too. But I admit I don't have an Evostar or any of these flatteners. Perhaps someone who owns either can give a more informed opinion.

Do consult the vendor about any spacing considerations. Depending on your camera you might need to get an extension ring or two, or the aforementioned adapter for a better fit. These things are far more important, missing the working distance by 5 mm (closer or father) can be catastrophic for image quality even if it is a 3000 dollar telescope+flattener on the other side.

Cheers,
Dimitris

Helpful Engaging Supportive

Jason Doyle Sr

Sep 25, 2020

On my 72ed, I used the "Orion Field Flattener for Short Refractors"… similar if not exactly like the OVL one. I was happy with it, considering its cost. My biggest gripe was the fact that it slides in and is held in place with the thumbscrews, rather than being threaded. I purchased a compression ring adapter, and wrapped on layer of electrical tape around the nose of the flattener to make the fit more snug. After that it was pretty solid. Most of the pics in my gallery are from this combo if you with to see some images regarding FOV.

Helpful Concise

ChrisWright

Sep 25, 2020

Jason Doyle Sr:
On my 72ed, I used the "Orion Field Flattener for Short Refractors"... similar if not exactly like the OVL one. I was happy with it, considering its cost. My biggest gripe was the fact that it slides in and is held in place with the thumbscrews, rather than being threaded. I purchased a compression ring adapter, and wrapped on layer of electrical tape around the nose of the flattener to make the fit more snug. After that it was pretty solid. Most of the pics in my gallery are from this combo if you with to see some images regarding FOV.

I second this. I also have the same Orion flattener and am very pleased with it.

Well Written Respectful

Debarshi Kumar Phukan

Topic starter

Sep 25, 2020

Jason Doyle Sr:
On my 72ed, I used the "Orion Field Flattener for Short Refractors"... similar if not exactly like the OVL one. I was happy with it, considering its cost. My biggest gripe was the fact that it slides in and is held in place with the thumbscrews, rather than being threaded. I purchased a compression ring adapter, and wrapped on layer of electrical tape around the nose of the flattener to make the fit more snug. After that it was pretty solid. Most of the pics in my gallery are from this combo if you with to see some images regarding FOV.
I second this. I also have the same Orion flattener and am very pleased with it.

Jason Doyle Sr:
On my 72ed, I used the "Orion Field Flattener for Short Refractors"... similar if not exactly like the OVL one. I was happy with it, considering its cost. My biggest gripe was the fact that it slides in and is held in place with the thumbscrews, rather than being threaded. I purchased a compression ring adapter, and wrapped on layer of electrical tape around the nose of the flattener to make the fit more snug. After that it was pretty solid. Most of the pics in my gallery are from this combo if you with to see some images regarding FOV.

Then i will also definitely go with it. If I coundn't find the orion one, should I opt the OVL one?

Jason Doyle Sr

Sep 25, 2020

Then i will also definitely go with it. If I coundn't find the orion one, should I opt the OVL one?

I'm certainly no expert, but I'd say it's a safe bet they are the same item, just rebranded.

Well Written Respectful

Matthew Proulx

Sep 26, 2020 · Edited: Sep 26, 2020

I have this scope with the OVL field flattener and the Orion field flattener and neither cure the field perfect but it is better than without. Without it images are horrid as you can see by my early photos.

Debarshi Kumar Phukan

Topic starter

Sep 29, 2020 · Edited: Sep 29, 2020

I have this scope with the OVL field flattener and the Orion field flattener and neither cure the field perfect but it is better than without. Without it images are horrid as you can see by my early photos.

Thanks. But what adapters to do you use for the OVL field flattener and the ED 72? I have a T ring for Canon EOS M48x0.75, but with it I can't connect my camera to the field flatterner.

Valter Reis | Observatório Astronómico dos Reis-OAR

Oct 1, 2020

I'm using an 72ED with the OVL flattener and I'm happy with it… So far!

Mason Steidle

Oct 1, 2020

The OVL flattener has a t-ring thread on the back so it will screw right into the front of your camera. The front has a 2" barrel that sticks right into the telescope.

Well Written Concise

Debarshi Kumar Phukan

Topic starter

Oct 1, 2020

Mason Steidle:
The OVL flattener has a t-ring thread on the back so it will screw right into the front of your camera. The front has a 2" barrel that sticks right into the telescope.

The front barrel fits nicely into the telescope. But the back of the flattener does not fit into my Canon EOS M48x0.75 ring. Do I need another kind of T ring?

Regards,

Debarshi

dkamen

Oct 1, 2020 · Edited: Oct 1, 2020

You need T2 to Canon EOS by the sound of it. T ring is 42x.75 slightly smaller than the M48.

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