Focal reducer/field flattener

[wasyoungonce]

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 (http://www.iceinspace.com.au/forum/focal%20reducer%20flattener)appear to say it's actually an extender?

I have also looked at the TV (http://www.iceinspace.com.au/forum/showpost.php?p=577748&postcount=1) 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.:shrug:

[DavidU]

Brendan, there is a really good article here..........
http://www.iceinspace.com.au/index.php?id=93,458,0,0,1,0

[wasyoungonce]

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 (http://ghonis2.ho8.com/052308AT127mmfocaltests.html) 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.

[DavidU]

His stars are great with the 127ED, also the star test is good.
I hope yours comes back this good !

[wasyoungonce]

Ahh yes..the stars in his field are flatter without a reducer compared to my scope as well!

[wasyoungonce]

Anyone used a WO type II with a 127ED or scope of similar FL (F7.5, 952mm)?

[troypiggo]

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.

[Moon]

I took this image with the Astro-Tech Field flattener. LINK (http://deepspaceplace.com/show.php?id=ngc6523b)
I've got a WO type II as well, but I don't think it's as good a match.
James

[JohnH]

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...

[Moon]

Correct.
Here is another image, this time with a bigger chip and the TSRCFlat2 (http://www.teleskop-express.de/shop/product_info.php/language/en/info/p4006_TS-2--Korrektor-fuer-Ritchey-Chr-tiens-ohne-Verkuerzung.html) flattener. IMAGE (http://deepspaceplace.com/show.php?id=ngc3372stl2) 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 (http://www.teleskop-express.de/shop/product_info.php/info/p1010_Universal-2--Field-Flattening-Lens-for-Refractors-f-5-to-f-8.html)

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

[avandonk]

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

[wasyoungonce]

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 (http://www.optecinc.com/astronomy/nextgen.htm) (.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 (http://www.iceinspace.com.au/forum/showthread.php?t=59346).

Selecting a FL reducer/flattener is more of a crystal ball operation than any absolute facts. Shee's who'd have thunk it.:confused:

[wasyoungonce]

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.:thumbsup:

edit:
I also saw a gent at CN post (http://www.cloudynights.com/ubbthreads/showflat.php?Cat=0&Number=3989356&page=0&view=collapsed&sb=5&o=all&fpart=3&vc=1&PHPSESSID=) (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.

[mldee]

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.

[wasyoungonce]

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.:question:.

[mldee]

OK, clouds willing, I'll try and pop off a couple tonight and post them here.

Cheers,

[mill]

You can borrow my WO pflat II Brendan.

[wasyoungonce]

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...:cloudy:...yeah like that will happen!

[mldee]

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,

[wasyoungonce]

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!:lol:

[GrampianStars]

What about the Orion unit
https://www.bintelshop.com.au/Product.aspx?ID=8586

[mill]

[QUOTE

I'll have to wait till I get my Lens back..and the clouds in Melbourne clear...:cloudy:...yeah like that will happen![/QUOTE]


Yep it doesn't look good for the coming week too.
I am getting withdrawal symptoms :(

[wasyoungonce]

To be honest I didn't even consider this one. :thanx:

I have read that it works well and it certainly would appear to suit regarding the FL. Although, like the TV unit I believe it needs adaptors for 2" ..I don't see any available?

It's also kinda in the price bracket of the WO & TV units...competition is stiff!

On a plus side it's rated as a .85X reducer which is probably around the reduction I was after..the "goldilocks" reducer...not too much...not too little.

[wasyoungonce]

Well....after much procrastination and penny pinching I purchased the TV .8 reducer RFL-4087 and accessories.

Why this one?...well...I wish I had the ultimate answer in few words but suffice to say...mfgrs name; accessories; reviews; but not price. Although I must say with the $Aust as it currently is..this tipped the hat.

I'll post back when I can do some tests.


Thanks for all the help gents.:thumbsup:

[mill]

Good luck with the test, raining now :(

[wasyoungonce]

Hi martin....Sigh! ..don't I know it :sadeyes:. It's the way of it.:(

[wasyoungonce]

Alright an update, all is not going well with the reducer! I have my TV RFL-4087 reducer/Flattener and new ML focuser, so I can now reach in-focus enough to use the reducer.

I have spaced it to 56mm (T ring shoulder to focal plane (http://www.televue.com/engine/TV3_page.asp?return=Advice&id=85)..just scroll down a little) which is correct according to TV site (http://www.televue.com/engine/TV3_page.asp?return=Advice&id=85#Distance) . I even called them to confirm that this is the method for measuring this spacing.

TV said that by using this FL reducer and their T ring adaptors will naturally achieve the correct 56mm spacing for a DSLR.

So I did all that and...no go. The stars are not pinpoint at the edges, they are not gross but they are not pinpoint either.

I suspect I may have to shorten this spacing..which will be a real pain. I found I can create a 1mm shorter T ring spacing by disassembling the TV T ring and building a Frankenstein version from the parts of other T ring adaptors.

So I'll fiddle with spacing and report back...in the mean time..pulling my hair out at the thought that this reducer may be incompatible with the 127ED!:eek:

[Visionoz]

So Brendan, how did the "frankenstein" version work AFA the TV reducer vs 127mm OTA work out?

Cheers
Bill

[wasyoungonce]

Well I still have some field curvature but I believe that is mostly due to focuser alignment as it is mainly in the lower 2 quadrants. The upper 2 are quite good at std spacing. I posted images of all this on the yahoo 127ED forum.

I have not had time lately to play with it.

But I get the feeling no flattener/reducer really works 100% with the 127ED triplet. Unless of course they (the OEM) release one.

I need to collimate my focuser and re-do the test. So I need a LASER to align it. Did anyone say...cash flow issue!

[Visionoz]

AAah! good to hear that it's actually workable!

The MoonLite you have can be collimated - I see!
Are you saying you need a normal laser collimator like those used in newts collimation? IF yes, PM me your address and I'll send you mine and you return that to me after you're finished with it - it's supposed to be collimated already etc and I've used it a few times on my 12" dob but it hasn't been used for anything else now for the last 8 months!!

HTH
Cheers
Bill

[wasyoungonce]

Hi Bill that's a kind offer.

PM sent.

Brendan

[wasyoungonce]

Heads up on progress.

Just used Bills LASER collimator and centre spot of refractor with lens off. Thanks a million Bill.:thumbsup:

LASER spot was 10mm left and 5 mm high (view from front of OTA), so yep focuser alignment was out.

All fixed now (adjusted the CFL focuser) so we shall soon have some results on the reducer again. I did note that applying around 2kg force to the draw-tube caused the LASER spot to move around .5~1mm. This is way more than my camera mass force but I didn't expect this.:shrug:

[wasyoungonce]

Ok the final word on the Televue RFL-4087 .8X reducer flattener on the 127ED.

It fails.

I aligned my ML focuser to the OTA using a LASER (thanks very for the loan from a fellow IIS member Visionoz) and the results, while improved are probably only acceptable in star elongation to around 70% out from the centre.

This image is a corner crop but it gives you an idea of the best I can wring from the reducer flattener. F6 imaging looks great with this scope (with the reducer fitted) you get a whole lot more sky real estate but the damn star elongation is a real off put. I'll still use it but crop out the offensive areas...which kinda negates the reason for a reducer.

Thus I do not recommend the Televue RFL-4087 .8X reducer for this scope. Looks like we have to wait for the OEM to get their act together. Sigh....(That was an expensive mistake) ...if ever at this rate.

regards

Brendan

[Visionoz]

Brendan

Are you sure your issue is not with finding the "ultimate" correct spacing for this reducer/flattener?

Cheers
Bill

[wasyoungonce]

Hi Bill.

I previously looked up the TV site and found the correct spacing which is 56+/-2mm. I even called TV USA on the phone to confirm this.

I also have the TV spacer kit TLS-2245 which has various spaces from 1mm, 2mm to 25mm and have tried combinations of these, photographically, unsuccessfully. I went so far as to make a hybrid T ring that was 1.5mm shorter focal path length and this didn't work as well.

I found the optimum spacing with the least star elongation was at the published spec distance. However, my stars are not pinpoint at this and are worse at any other spacing distance. At this optimum spacing they are not grossly elongated at the edges, in fact they are probably better than the native focal length edge stars.

I purchased this unit as others had reported that the other major FL reducers like WO etc did not work with the triplet. The Astrotech type II and Hotech field flatteners apparently work very well but I was after a reducer flattener.

I got to say...at F6 the image FOV is ..to coin a phrase "most excellent" and enticing.

I'll still use the reducer but crop out the offensive areas which kind of negates the usefulness of the reducer.:sadeyes: