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Old 17-08-2010, 04:29 PM
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wasyoungonce (Brendan)
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Focal reducer/field flattener

When I get my lens cell back from my 127ED (F7.5).. I'll be in the market for a Focal reducer field flattener of around .8x reduction.

I have looked at the WO type VI but am unsure if it is actually a reducer. Some advice appear to say it's actually an extender?

I have also looked at the TV RFL-4087, which appears to fit the bill although a little expensive considering the adaptors needed.

So should I go for the WO type VI unit or the TV unit? I am not looking at the WO type II as I believe it's mainly for around 600mm FL scopes.

Any advice appreciated...especially anyone who has either reducers/flatteners.
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Old 17-08-2010, 05:43 PM
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Brendan, there is a really good article here..........
http://www.iceinspace.com.au/index.p...93,458,0,0,1,0
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Old 17-08-2010, 06:33 PM
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wasyoungonce (Brendan)
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Thanks David. I have seen others using the Celestron (or Meade) .63 reducers on refractors and getting good results. Although these were made for the SCT so I have to ask..how can this be?

Gary Honis did a test of reducers with his 127ED. The Celestron .63 and the TV .8x (for 600mm scopes, not the RFL-4087 unit). He showed the Celestron reducer to be quite good. The TV unit (similar to the WO II) was asking too much for the scopes FL of 952mm. This backs up the IIS test you linked to.

But I get the feeling the best one is the TV RFL-4087...although not the cheapest. Although I'd love to hear from users of the WO type VI reducer/flattener.
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Old 17-08-2010, 06:42 PM
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His stars are great with the 127ED, also the star test is good.
I hope yours comes back this good !
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Old 17-08-2010, 06:51 PM
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wasyoungonce (Brendan)
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Ahh yes..the stars in his field are flatter without a reducer compared to my scope as well!
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Old 17-08-2010, 10:20 PM
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wasyoungonce (Brendan)
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Anyone used a WO type II with a 127ED or scope of similar FL (F7.5, 952mm)?
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Old 18-08-2010, 06:25 AM
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I've got the WO FF IV. It does give me a flat field with 40D on ED80, but as you say it isn't a reducer. It actually does extend by around 1.1x-1.15x.

Can't help with the others. I've only ever tried a MPCC, WO FFIII and WO FFIV.
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Old 18-08-2010, 07:01 AM
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I took this image with the Astro-Tech Field flattener. LINK
I've got a WO type II as well, but I don't think it's as good a match.
James
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Old 18-08-2010, 08:40 AM
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Brendan,

I have tried a WO flat III with the ED127 - it is not recommended - it over corrects, remember the 127 field is reasonably flat to start with (or should be!).

I have a WO II as well (for my 66ED) but I tried it with the 127 for fun - that is also a no-go.

The Flat IV I have not tried - I think there were issues with the early models hence the non-reducing feedback - I am not sure but I suspect current models would be ok.

The Astro-Tech seems to be well regarded by 127 owners with DSLRs but I think is a pure flattener (James is that right?) and not an FR, the latter was more important for me (I have a small ccd) so I have gone for an Optec model....

Remember spacing is critical so your results will be different than mine depending on your imaging train. If you have an OAG and FW in line (as I do) the ideal additional spacing may be -ve with some units which rules them out...
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Old 18-08-2010, 10:11 AM
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Quote:
The Astro-Tech seems to be well regarded by 127 owners with DSLRs but I think is a pure flattener (James is that right?)
Correct.
Here is another image, this time with a bigger chip and the TSRCFlat2 flattener. IMAGE Even though it's not designed for this scope, I think it does a reasonable job. For regular sized DSLR chip it would be fine. Teleskop Service also have one designed for refractors that I have not tried but I think it would be worth a shot : TSFlat2

The only thing I don't like about the Astro-Tech is the small T2 aperture. There is less vignetting with the full 2 inch TS ones.

James
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Old 18-08-2010, 10:50 AM
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You are welcome to try out my Hutech #7887 0.85 FR/FF. It is fully adjustable for focal length by simply changing spacers so it is very stable. It works very well on 80ED, 100ED and even a 150mm F5 Achro. It illuminates a full frame very well without vignetting. Just PM me for details as you are only 17km away.

Bert
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Old 18-08-2010, 10:56 AM
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wasyoungonce (Brendan)
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Thanks gents, especially thanks for the links. It makes for good comparison.

I kinda disregarded the WO type III as it appears to only suit a few scopes. The Type IV appears to flatten well but some do not appear to reduce.

What I wanted was to flatten and give a faster FL...exposure time.

The Astrotech reducers look good as well but I read mixed reviews. The Astrotech version looks like a WO type II. I also wonder if the WO II would work?

I have looked at the Optec NGUW (.7X). It appears good but not a flattener and limited to 18mm ccds..aka for Sbig ccds.

I think DavidTrap has a TV RFL-4087 as he tested one here.

Selecting a FL reducer/flattener is more of a crystal ball operation than any absolute facts. Shee's who'd have thunk it.
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Old 18-08-2010, 11:00 AM
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wasyoungonce (Brendan)
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I've had many kind offers from James & Bert,..I feel like from a pauper to an embarrassment of riches!

Thanks gents I'll definitely seek help...if & when my lens cell returns.

A big thanks to all.

edit:
I also saw a gent at CN post (post #3987593 ) that he uses a TV .8x reducer/flattener. His post, literally minutes before mine (here), was impeccable timing! I've asked him a few questions as well.

edit 2:
I asked Explore Scientific and they said they have one in the mill but some time off yet. ES said they have been told the TV or Astrotech reducers work but have not tried them themselves.

Last edited by wasyoungonce; 18-08-2010 at 02:39 PM.
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Old 19-08-2010, 11:35 AM
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Brendan, I bought a new WO FR IV from their web shop a couple of months ago. I'd be happy to take a set of "with and withouts" using my QHY8 with my Megrez 80mm if it's of any use for you in seeing whether it reduces or not.
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Old 19-08-2010, 12:19 PM
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Quote:
Originally Posted by mldee View Post
Brendan, I bought a new WO FR IV from their web shop a couple of months ago. I'd be happy to take a set of "with and withouts" using my QHY8 with my Megrez 80mm if it's of any use for you in seeing whether it reduces or not.

Actually that would be excellent Mike. It's well known it flattens very well...but I'm sure I'm not the only one curious if it actually reduces as well..
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Old 19-08-2010, 03:30 PM
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OK, clouds willing, I'll try and pop off a couple tonight and post them here.

Cheers,
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Old 19-08-2010, 05:06 PM
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You can borrow my WO pflat II Brendan.
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Old 19-08-2010, 06:15 PM
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wasyoungonce (Brendan)
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Thanks Martin...I wouldn't mind trying it as well. Although the FL of my 127ed is probably a little long.

I'll have top wait till I get my Lens back..and the clouds in Melbourne clear......yeah like that will happen!
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Old 19-08-2010, 06:53 PM
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WO FR IV reducer comparison

Looks like my FR IV reduces, I haven't bothered making any exact measurements.

Pix below were taken at twilight in order to post them asap, bit of smoke haze around. Both are 5x stacks with 5s exposure in Neb, and levels adjusted in neb and then saved as jpg's. Used Paintshop to reduce the jpg's by 75%. Pixel measurements are the same, 760 x 503.

I forgot to note the centre star, I think it's Eta Lup. Both pics taken within 2 mins with no scope recentering needed.

Note: No FR needs approx 8" of back focus with QHY8, with FR IV, direct connection plus 50mm T extender from FR to QHY8, so this would be a bonus in not needing the longer back appendages to gain focus with it. The FR pic also looks better

Hope this helps. Let me know if you want the RAW pics for better measurement.

Cheers,
Attached Thumbnails
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Click for full-size image (WO with FR small.jpg)
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Old 19-08-2010, 07:10 PM
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wasyoungonce (Brendan)
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Thanks Mike you can see the reduction and faster acquisition of photons on the sensor.

I've got to wonder why WO does not post this data or comparison pics on their website? So that definitely puts the WO type 4 on the contender list.

Once again thanks...and it's nice to see a clear sky for once...even if it is in a pic!
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