Flattener recommendations?

[Anweniel]

Can anyone help me make a decision as to the appropriate field flattener for my Megrez 90?

The focal length is 621mm

Focal ratio is F6.9

I looked at the William Optics AFR-IV 0.8 reducer flattener IV http://www.firstlightoptics.com/reducersflatteners/william-optics-afr-iv-08x-reducer-flattener-iv.html which says recommended for 500mm -1000mm fl

TS Universal 2" flattener http://www.365astronomy.com/ts-universal-2inch-field-flattener-for-refractors-from-f5-to-f8-p-3080.html

which says recommended for F5-F8

Williams Optics mkIII 0.8 reducer/flattener

Hotech SCA Field flattener http://www.firstlightoptics.com/reducersflatteners/hotech-sca-field-flattener.html

which says recommended for F5-F8

And theres a few others too but I can't decide which is the most appropriate! I think I would prefer to take a dedicated flattener without reducing the focal length. The Hotech looks the most inviting but its a lot of money to go on something that is clearly so sensitive so want to make a good choice before splashing any cash.

Any help most appreciated

[ronin]

There is someone on SGL that has taken some good images with a Megrez 90, but the post was some time back, cannot recall the name so cannot read their signaure to see if they list a flattener.

I would half suggest you PM a mod and ask them to alter the title/subject to Include "Megrez 90" at the start as it may catch their attention more.

[Dave Smith]

I have a TEflat2 flattener for use wth my Megrez 90 and it works well. It is a dedicated flattener and not a reducer. I can send some test images if you like using a modified Canon 40D.

I also use a WO 0.8x reducer III(2011) which is supposed to be suitable for the Megrez 90 and Megrez 72. I have used that successfully with my Megrez 72 but cannot find any M90 images taken with that.

Dave

[alan potts]

I would say with the WO flattener myself at least you know the optical quality will be to the same standards.

Alan.

[Anweniel]

Thanks for the replies, Dave I am very interested in your test images would be very kind of you if you dont mind sending me your results. I am not adverse to using a reducer its more that I am just used to using the scope at its native 621mm and I enjoy the FOV it provides. There is a type III WO reducer/flattener on AB&S so if you do find any results for your M90 + type III combo that would be interesting too.

Thanks again

[Dave Smith]

I don't have the time this evening but if you are a member of PAIG they can be seen here http://www.progressiveastroimaging.com/viewtopic.php?f=24&t=4766

otherwise I can do it in the morning.

Dave

[Anweniel]

Thats ok Dave no rush I'm not a memeber of PAIG but I'll see if I can have a look there. Thankyou

[Anweniel]

Managed to check out your crops using the TE flattener Dave looks like it did a pretty good job across almost the entire field.

[Dave Smith]

I'm pleased you managed to see them. I bought and use my WO III 0.8 reducer to use with my Atik 314L+ CCD camera and with that as it has a much smaller chip the flat field aspect is less critical and it was the reduction that I was getting it for.

By the way, the spacing required with the TE flat2 is 129mm as advised drectly to me by Teleskop Express. Apparently this spacing is not critical.

http://www.teleskop-express.de/shop/product_info.php/info/p1010_TS-Flattener-fuer-Refraktoren-universelle-Bildfeldebnung-von-f-5-bis-f-8.html

Bern at Modern Astronomy sells TE kit and is often cheaper.

This flattener also worked well with my FL102S scope which is f8.8

Dave

[Anweniel]

Great thats just the info I was after. I mailed the chap about the WO III reducer/flattener and if he is willing to sell to me at the price I offered its probably worth a shot to see how it goes, I could always sell it on I guess if it doesn't marry up well with the camera chip. It is a significant saving on the TE and Hotech flatteners though so if it works out I'll have saved myself a fair bit, if not I think I'll need to hang until after christmas!

Thanks again Dave

[Coco]

I would be careful about speeding up that scope, my WO 110 megrez didnt like reducers much ( WO MKIII & IV) but was ok with the WO MKII , when I

say Ok I mean with a small chip ccd.

The best results I had were with one of these..

http://www.firstlightoptics.com/reducersflatteners/skywatcher-field-flattener.html

[Ransu]

I have took some test images with Megrez 90/ Canon 600D and several flattener/reducers.

TS Flat works quite well with every scope i have test, also with Megrez90.

You can find test images from here. https://picasaweb.google.com/106884738215780458002/ReducerTest

Folder includes total 49 test images with several scopes and DSLR

[Anweniel]

I would be careful about speeding up that scope, my WO 110 megrez didnt like reducers much ( WO MKIII & IV) but was ok with the WO MKII , when I

say Ok I mean with a small chip ccd.

The best results I had were with one of these..

http://www.firstligh...-flattener.html

Thanks Coco, I must admit I do prefer the thought of a dedicated flattener than flattener/reducer. Its a little odd that the Skywatcher gave you the best results as it is apparently designed for F5.5-F6 scope, F7 is quite a big difference from this. Goes to show how you just don't know until you try these things out! Since I am imaging with a DSLR the chip is quite large so presumably more sensitive to good correction.

I have took some test images with Megrez 90/ Canon 600D and several flattener/reducers.

TS Flat works quite well with every scope i have test, also with Megrez90.

You can find test images from here. https://picasaweb.go...002/ReducerTest

Folder includes total 49 test images with several scopes and DSLR

Thanks Ransu, this really confirms what Dave has found

[DaveS]

Well I've just got the WO Reducer / Flattener IV to go with my M90 and 550D

Hope it works.

If it's clear tonight I'll try and get some images, but as I'm just starting AP they may not be up to much anyway.

[Anweniel]

Be good to see how you get on mate

[DaveS]

No joy, thin high cloud came over so I packed up.

[Anweniel]

Seem to have forgotten my PAIG username.... doh! but I can show here some recent results with the Hotech SCA flattener.

I found the WO Mk III FF/FR just didn't work with the Megrez 90 and there was a tremendous amount of egg like stars in the outer 30% ish that was obvious to the naked eye. The Flat2's price tag put me off and I plumped for the Hotech one as it was advertised on FLO as suiting a good range of F/ratios (F5-8) which the Megrez seems to fit nicely in the middle of at F6.9.

The self centring is an added bonus and apart from the obvious advantage of centring the imaging train it also provides added rigidity to the system. The thumbscrew on the focusing draw is more or less redundant as the SCA device is enough to hold the weight of both the adapter itself and the DSLR on the back of it! Naturally I continue to use the thumbscrew too but its a case of 'belt and braces' to my mind.

Here is the a recent single 10 minute frame that I have stretched in levels and curves a little to darken the background and highlight the data. Hopefully this demonstrates the capability of the combination of flattener and OTA and I highly recommend this marriage to other Megrez90 owners. The main image is uncropped and there is a crop of each corner to show performance at the most vulnerable areas.

Hope this is of use to anyone

Full frame (Canon Eos 1000D unmodified)

Crop top left corner

Crop top right corner

Crop bottom left corner

Crop bottom right corner