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rocketandroll

Field flatteners for WO Megrez 72?

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Hi folks

So, after doing some first test images with the Megrez 72 a month or so ago it became obviously apparent it needed a field flattener badly as 40%+ of the field had odd shaped stars.

So, I got a SW flattener... one of these:

First Light Optics - Skywatcher Field Flattener

Great... but it seems to have little or no noticable effect on the useable area of the image?

Am I asking too much? should I have to do a detailed analysis of the images to notice any tiny difference?

If this doesn't work... does anyone have any suggestions of another flattener which might? Anyone else got a meg72 who can tell me what they use?

I'm using a DSLR btw, so need a LOT of the field to be flat with such a large chip.

Ben

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I'm using a WO FFIII on the Megrez 72 with Canon APS-C Sensored DSLR's...

Some would argue (rightly) that it's not the best option now .. but I can live with it...

Focus is critical for "decent" corner stars when your usign it...

Peter..

Peter...

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I'm using a WO FFIII on the Megrez 72 with Canon APS-C Sensored DSLR's...

Some would argue (rightly) that it's not the best option now .. but I can live with it...

Focus is critical for "decent" corner stars when your usign it...

Peter..

Peter...

I had a WO AFRIV which I tried using with my ED80 but couldn't ever get it to focus so sent it back... that states it's for use with scopes in the 500 - 1000mm fl range, beyond the 432mm fl of the Meg72 so I assumed it wouldn't work.

Since some kind person sent me a Bahtinov mask for the Meg focus shouldn't be a problem :-)

Was the FFIII suited to shorter focal lengths too? Or is finding anything specific to such a short fl scope always gonna be a compromise?

Ben

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When I bought my Meg72 a good few years agao there wasn't so much choice so I had a word with Ian King and seeing as i was thinkign of getting some of the larger Megreaz scopes in the future we "plumped" for the FFIII for a bit of longevity...

It's not optimal and as I said early is really really fussy about focus slightly out either side and you go from sagittal to radially stretched stars in the corners.. before the arrival of the "bahtinovs" it was a nightmare but not impossible... I use the Bahtinov grabber app with it..

It is well built and the rotation mech is nice and smooth... I use it with a 2" pushfit connection on which leave a Hutech IDAS P2 LPR filter on its noespiece...

Here's a link to one of my pics with it...

https://picasaweb.google.com/PsychoBillyUK/PublishedAstrophotosOnesThatHaveMadeItIntoPrint#5361005460195561506

Have a look at the PDF user Manual http://www.williamoptics.com/support/download/megrez72.pdf p13... FFIII for Megrez 72,90 and 110

Peter...

Edited by Psychobilly

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Cheers Peter.

The Meg72 brochure there does specifically mention those flattener/reducers... obviously they're now no longer available, so the AFR4 seems the only option... wonder if it'll work?

Might drop WO a line, see what they say.

Certainly dropping it to f5 or just below would be nice too :-)

Ben

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Hi all

Ok, I'm worrying myself now that I am doing something wrong or that there is a problem beyond the flattener I have not being ideal for the scope...

So, can someone take a look at the enclosed and tell me if this looks right?

This is a crop of one quarter of a full frame from my Eos 500D of the NAN from the other week.

The center lines show the center of the full frame and the circle shows roughly where I think the useable image stops and the manky star shapes start. The circle covers abouy 25 - 30% of the full frame... which is IMHO absolutely useless.

This is of course scaled to about 50% of full size... but the dodgy stars show up fine at this size.

So... is this what I should expect from a fairly high-end refractor with a flattener? Or is this really as bad as I think?

I'm still trying to get advice on what (still available) flatteners/reducers will work with this scope... so far three people have recomended the WO FFII to me, which is no good because you can't get them any more!!!! :-)

Thoughts?

Ben

post-23494-133877677073_thumb.jpg

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The distance from your sensor to bayonet on the canon is 43.5mm so you need another 10/11mm space then the focal reducer for it to be in the optimum area.

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That extra space comes from the EOS-T adaptor...

The T adaptors were originally for use with "T mount lenses" these were 3rd party lenses that were designed to be used (with a suitable t-ring) on a wide range of different camera bodies with widly differing "registers" (the distance from the lens mounting flange to the FP of the camera)..

The Register of any Camera body fitted with a matching T-Ring will be 55.0mm

Peter..

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I am no expert on nice rounded stars, I can't get them for love nor money! But in my quest to get them, I have spent ages looking at frames and trying to work out problems.

I may be TOTALLY wrong, and so I hope someone else will come along to think about this, but it will give another possibility.

The area that you have highlighted where the stars are nice and tight is in a circular area, could it be that the focuser isn't sitting straight in the tube of the OTA, or that there is some focuser sag? From the image you have submitted, it almost looks as though your camera is pulled down and slightly left - I would expect in a perfect world for the circle you have highlighted to be pretty central and if the issue were the reducer / flattener then you'd be seeing 4 bad corners and a nice circle of good focus- Does that make sense?

As I said though, I am a learner, bimbling my way through the minefield that is a flat field and failing spectacularly at the moment.

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Did you see the heads up about a FF-II on Astro Buy and Sell.. I guess it wouldn't have hung around for very long...

Peter...

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Thanks all for the thoughts....

@Swag: Sorry, I should have explained, I only posted one quarter of the image for the purpose of file size, every corner is the same in that at about the same distance from the center the stars are elongated away from the center of frame. It did occur to me to see whether this was a non-symetrical problem of sag or similar, but the effect is symetrical (give or take) around the frame.

@Peter: So you are saying the flattener IS automatically at the correct distance and a spacer won't help.

In that case, I assume everyone agrees this is not right and I need to be looking for another flattener reducer then?

In which case we're back to the original problem... which one?! :-)

Ben

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Yes(ish)

The WO reducers when used with DSLR's are designed to have a t-ring fitted and attached directly to the camera body...

The reason that I am saying yes(ish) is that they say the spacing should be 56.0mm and the T-mount standard is 55.0mm so there is something I need to "investigate"...using a 1.0mm spacer washer between the Reducer and the tmount if there is enough thread to accomodate it "safely"... I have a range of different shims i could try...

What software are you usign for Post processing..

The lens correction tools in CS can make a big difference at the expense of a reduced FOV... The "location" of Lens Correction tools moves around a bit depending which version of CS your using...

Upload a full frame image somewhere and send me a link and I'll have a look at it later...

Peter...

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Hi Ben,

Woops didn't realise that, sorry!!

Hope you get it sorted - I shall watch with interest.

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Cheers all

Peter, I'll e-mail you a copy of the full frame. I'm using Photoshop 7 at the mo (yes seriously) waiting to upgrade to CS5 shortly.

I am now worried enough about this, and the fact no other Meg72 users seem to have this issue that I have e-mailed the images to WO to see what they suggest.

And no, didn't see any note about astro buy/sell, and yes, seems it sold instantly :-)

Cheers

Ben

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Ok.... still worried about this.

Can anyone else who has used the Meg72 with an SW flattener and a DSLR send me a full res (or at least mostly full res) full field shot through it to compare?

It really concerns me that at least three people now claim to have got good results from this combo and mine is still dire?

Could it really be an issue with the scope? if so... what?

Ben

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There's a Televue 2008 available just now which is ideal for 400 - 600mm focal length scopes.

It is one of the best as long as your focuser can take a 2" push fit?

I use one and it's great...

Cheers

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DARNIT!!!!

Why do these things always come up for sale just after you've ordered something new?! :-)

I just ordered a WO FF3, should be here Monday/Tues... was gonna see if that worked any better.

I could be really cheeky and try and get the Televue as well then just see which works best?

My concern at the moment is that it's the scope that has the problem and no flattener, no matter how expensive, will fix it?

Ben

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the 72 is highly regarded so i don't think it should be a problem, a good flattener should help though.

Cheers

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How flat does your TRF-2008 make the field using say your Canon 5D?

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I've never used it with the full frame 5D. I'd say something APS sized would be ok but I can't yet vouch for a full 35mm sensor.

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Hi rocketandroll,

Sorry I am a bit slow catching this thread.

I to have the SW FF on a Megrez 72.

It's a long story but I've had it a while, but only used it tonight. I found pretty much the problems that your are having. I have the radial stars in thee corner of my frame. Not what I was expecting from an FF :)

Also I find it won't focus properly at least not with BackyardEOS. I tried focusing on Jupiter (its very small on a 1.6x sensor) but I couldn't get a good sharp picture. I'm a bit of a novice so may be it was the seeing that was making it blurry?

I'd be interested to hear if you get any other field flattener working.

In the meantime I have an SW FF for sale. Any takers??

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i had a look at the pic and i cant see anything major wrong with it at that reduced size, there does seem to be some slight elongation in the stars but only very slight which could be slightly focus or star trailing (by a few seconds).

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I also have the megrez 72mm & the flattener with the same results. Its a pain in the backside as its £60 wasted. Wish i hadnt bothered with it. Not sure if i can return it to the supplier - FLO i think as ive had it for a couple of months now, but only just been able to test it...

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BUMP!

Anyone tried the new WO Flattener 6 with the Megrez 72?

Being largely unimpressed with reviews of and images from TS apos I have decided to Guide with an OAG and use my Megrez 72 'guide scope' for wide field imaging. I used to own the MkIII flattener but was unimpressed, like others I found the stars misshapen even at the correct spacing.

Thanks

DD

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