97 replies to this topic

[Messyone]

There have been many threads on which scope/eyepiece combo to use for wide field. Being a wide field junkie I've been on my own search to find affordable wide field enjoyment with a telescope. Enter the TS 2" FF....have thought about this one on and off for a few years. Teleskop Express used to call this for visual and AP use, but dropped the visual part for some reason. CN member doctodub? or is it doctordob....can't remember, mentioned using it for visual and how well it worked in a very recent thread, so I bought one. To make the decision easier the price used to be 225Euro's but was down to E155....the buy button was pressed.

 

I have 3 scopes I like for WF. 102mm f5 Celestron with GSO Crayford upgrade, 80mm f7.5 Achro used as a WF on my 6" f12 Refractor and a 60mm Sharpstar ED.

 

The specs for the flattener say for the 102 f5 I need 118mm light path for the FF to work, 113 for the 80mm and 128 for the 60ED.

 

For this I used 4 eyepieces, Pan 41 Pan 35 ES 34 68 and Agena Astro SWA38. Did comparisons with and without the FF. The Diagonal is a GSO 2" Dielectric. I measured the light path of this diagonal to be 113mm....a lucky number as it happens! 

 

After a number of nights my result so far is:

 

The winner is the 80mm + FF and the Pan35. Pinpoint to the edge, very nice view at 4º TFOV. In the same scope with FF Pan 41 vignettes badly, ES34 has edge issues from 80% out, ditto the 38SWA. Take out the FF and the Pan 35 is still the best view 80% out with a bit of FC visible. 

 

4" f5....no real difference for some reason with or without the FF....best is the Pan 41. Widest with nearly pinpoint stars at the edge. This is probably more to do with the lack of magnification but good is good. Next the 35, good to 80% out.  ES34 good to 70% out and 38SWA bringing up the rear and not worth using, seeing as the Pan41 is so good.

 

Haven't got around to the ED60 yet....more to come. I need to muck about with spacing for the 4" f5 too...118mm might not be the best.

 

So far I'm very happy with the TS 2"FF as I really bought it to use with the 80mm f7.5. Turns my cheap preloved  Achro into a nice WF scope, as long as I stick a Pan 35 in the focuser. The focuser being the weak point of this scope. The usual pincushion is evident, not that I'm bothered by that.

 

Photo's of the scopes in question and the FF on the diagonal.

 

 

 

 

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[nicknacknock]

I would have figured that the 4" would stand to benefit the most - faster objective and all. Can you elaborate a bit more on the Pan 35mm and 80mm f7.5 combination? Based on your perception, how significant was the difference?

[Messyone]

I would have figured that the 4" would stand to benefit the most - faster objective and all. Can you elaborate a bit more on the Pan 35mm and 80mm f7.5 combination? Based on your perception, how significance was the difference?

The Pan 35 and 80mm f7.5 seem to be the perfect combo to my eyes. I have not looked through a TV 101 so have no comparisons to make with a 'true' flat field scope. So I see pinpoint stars to the edge, a slight drop off in illumination at the edge too....I wonder if the long draw tube, 4", is vignetting this scope as I have the focuser racked nearly the whole way in. When panning around I see the classic pincushion distortion. I see the same pincushion when I take the TSFF out and FC too.

 

So quite a difference, as I said this combo makes the TSFF well worth it for me. My 6" f12 has pinpoint stars to the edge in just about every eyepiece I'v tried, so I am a bit fussy on this front.

 

Anyone have the TV101 and a Pan35? I'd like to know if pincushion is visible.

 

The 4" is a work in progress with spacing...

[Magnitude7]

So I see pinpoint stars to the edge, a slight drop off in illumination at the edge too.

 Sharp eyes.  In all the times I have read comments regarding the 35mm Panoptic, I have only read that once.

Yes, there is an obvious drop off in edge illumination with the 35mm Panoptic.  I see it any telescope I put it in.  It comes from the eyepiece, not the telescope.

[Messyone]

After much stuffing around withe the 4" f5 I could find no ideal spacing.....a slight improvement on no FF but not worth the trouble. Same goes for the Sharpstar ED 60 f5.5 

 

So my conclusion is it works visually at 600mm fl but not on any other focal lengths. The 80mm f7.5 is now a perfect wide field scope. Shame the 4" doesn't work. 

 

I suppose it works for cameras but have no idea on that.

 

Matt

[doctordub]

Hi Matt it is doctordub, I am glad you were able to get the right spacing for your 80mm. Here is my previous post:

 

"I have an APM LOMO 80/480 Super Apo. These scopes are out of production, but can be found used from $700-$1300 used. You could also get a new Stellarvue 80/480 triplet Apo for $1195.00. With my APM LOMO 80/480 I get these TFOV: with my Panoptic 41mm=5.5 degrees, Nagler 31mm= 5 degrees, and Ethos 21mm= 4.5 degrees. I have found an easy fix for the field curvature Jon is pointing out. TS Optics has a Flattener that can be used for visual use. I thread it onto my TeleVue 2" Everbright diagonal and scores of previously invisible faint stars pop into focus. My eyes accommodate the bright stars so I was surprised to see this effect!.

TS Optics field flattener for Photo and Visual with a generous spacing:
♦ Focal length < 450 mm: 128 mm
♦ Focal length 450-490 mm: 123 mm
♦ Focal length 500-550 mm: 118 mm
♦ Focal length 560-590 mm: 116 mm
♦ Focal length 600-690 mm: 113 mm
♦ Focal length 700-800 mm: 111 mm
♦ Focal length ab 800 mm: 108 mm"

 

I have only used the flattener on my 80mm Apo that is 480mm fl."

CS

Jonathan

[Messyone]

Hi Jonathon and thanks for the TS recomendation for visual. For me the TS FF works with my 80mm f7.5 Achro with Pan 35 beautifully. A stroke of luck pehaps that it does as that is the combo I bought it for. 
 

For anyone interested:

 

http://www.teleskop-...refractors.html

 

 

 

[Kent10]

I just acquired a Lomo 80/480 and based on your recommendation, Jonathan, I also ordered the TS Flattener.  Thanks for sharing your experience.  I hope to try the scope and flattener sometime soon.  Can't wait.

[Peter Besenbruch]

Hi Jonathon and thanks for the TS recomendation for visual. For me the TS FF works with my 80mm f7.5 Achro with Pan 35 beautifully. A stroke of luck pehaps that it does as that is the combo I bought it for. 
 

For anyone interested:

 

http://www.teleskop-...refractors.html

I am interested, and I ordered one for my C80ED with 40mm Pentax XL.

Edited by Peter Besenbruch, 17 February 2017 - 12:42 AM.

[tony_spina]

Will this work well with the ES 127AR?  D:127mm, FL:826mm, F/6.5

[Ernest_SPB]

Hm... such two-elements flattener must be optimal for one exact focal length introducing over correction for longer and under correction for shorter.

[Messyone]

 

Hi Jonathon and thanks for the TS recomendation for visual. For me the TS FF works with my 80mm f7.5 Achro with Pan 35 beautifully. A stroke of luck pehaps that it does as that is the combo I bought it for. 
 

For anyone interested:

 

http://www.teleskop-...refractors.html

I am interested, and I ordered one for my C80ED with 40mm Pentax XL.

 

Hi Peter, I'm really interested to know how you it works with your ED 80. I presume it's 600mm/f7.5. The Pan 35 is the only eyepiece I own that produced pinpoint stars to the edge. 

Matt

[Peter Besenbruch]

 

I am interested, and I ordered one for my C80ED with 40mm Pentax XL.

Hi Peter, I'm really interested to know how you it works with your ED 80. I presume it's 600mm/f7.5. The Pan 35 is the only eyepiece I own that produced pinpoint stars to the edge.

I'm not looking for pinpoints to the edge. I am looking for a reduction of curvature. I am hoping it results in an improvement. I own two, f7.5 refractors, an 80mm and a 120mm. The 120mm is fine as is. The 80mm is worse when it comes to wide fields of view, because of field curvature. I was intrigued when you achieved your results:

 

1) With so little effort

2) With an 80mm, f7.5 scope

3) With a GSO, 2", dielectric diagonal

 

It sounds like I might have a drop in, no fuss flattener for my 80mm, f7.5 refractor and GSO, 2", dielectric diagonal. That could be a lot of fun.

[Peter Besenbruch]

My flattener arrived and the clouds cleared away, though it stayed pretty windy. I took my C80ED out, kitted out with the field flattener screwed into my 2", GSO, dielectric diagonal. The eyepiece used was my Pentax XL 40mm, for 15x. I tested on the belt and sword of Orion, Sirius, M41, and M35.

 

Without the flattener I noticed some field curvature and some edge astigmatism. With my 61 year old eyes I could compensate for the curvature, but it was an effort. With the flattener, the curvature vanished, and the edge astigmatism looked more pronounced. That said, the image looked very nice indeed over 90% of the field. You could reduce the edge astigmatism quite a bit by the way you held your head when looking through the eyepiece.

 

There was almost a quarter turn difference in focus with and without the flattener.

[Messyone]

Hi Peter,

Can you get hold of a Pan 35 from anyone? As I mentioned it's the only eyepiece I tried that worked to the edge. All the others ES 34 68 SWA 38 Pans 41 and 27 didn't make the grade. There may be other long fl eyepieces that work.

Ernest SPB has it right that for visual there is an optimal focal length where it works.

Matt

[Kent10]

How important for visual is it that the TS flattener be at a specific distance?  I see Jonathan threads his onto a 2" TV diagonal but other diagonals might be different.  I tried mine with a TV and AP Maxbright diagonal only briefly so far on my 80mm F6 and it seems to flatten the field only for some eyepieces. 

 

I still need to do much more testing, but I think it flattens the field for the 30mm and 40mm Pentax XW but not for the Nagler 31mm or 30mm Leitz.  I also think it worked for the 21mm Ethos. 

 

I also found the flattener narrows the FOV slightly so I assume the power must be slightly higher.

 

Thanks, Kent

[Peter Besenbruch]

Can you get hold of a Pan 35 from anyone? As I mentioned it's the only eyepiece I tried that worked to the edge. All the others ES 34 68 SWA 38 Pans 41 and 27 didn't make the grade. There may be other long fl eyepieces that work.

Ernest SPB has it right that for visual there is an optimal focal length where it works.

No, no-one I know has one, and I have a perfectly good 40mm. The 35mm is simply too narrow. The people I observe with, if they have the money, tend to buy Ethos. If they don't have the money, they use that 25mm eyepiece they got bundled with their last scope (purchased in 1972), with a 9mm Kellner they got from somewhere for high power.

 

When Ernest mentions over, or under-correction, I think he is mentioning spherical aberration, and that isn't an issue here. I am getting edge astigmatism. The eyepiece has always had a bit of it. I did some careful checking. Yes the edge astigmatism looked more pronounced, but I think that's because the field curvature wasn't there. Overall, looking around a star field was a nice, comfortable experience. Moving Sirius from center to edge was the sterner test, and it was easier to compare before and after views. Again, Sirius stayed focused with less eye strain until the final 10%.

 

So, I will be using the flattener to look at wide fields with both the 40mm and the 22mm LVW. The field flattener is doing its job.

Edited by Peter Besenbruch, 23 February 2017 - 10:17 PM.

[Ernest_SPB]

When Ernest mentions over, or under-correction, I think he is mentioning spherical aberration, and that isn't an issue here. I am getting edge astigmatism.

 

No I have meant field aberrations.

 

Most probably this flattner is two-lens afocal system. It introduces small portion of spherical aberration and corrects astigmatism and curvature keeping the same level of chromatic aberrations. For longer focal length refractor this corrector (in the same position from focal plane) introduces too much astigmatism and curvature compensation (overcorrection) and it is recommended to move it a bit closer to focal plane making optimal astigmatism and curvature correction. But aberration balance becomes different and their correction is broken. Mostly and an issue is coma.

 

So the flattner works fine (excluding small portion of spherical aberration) in quite narrow range of focal length.

 

By the way, note that...

- three lens flattner corrects field aberrations without introducing even a sign of spherical aberration

- both type afocal flattners are quite sensitive to distance from focal plane

Edited by Ernest_SPB, 24 February 2017 - 10:38 AM.

[Peter Besenbruch]

 

When Ernest mentions over, or under-correction, I think he is mentioning spherical aberration, and that isn't an issue here. I am getting edge astigmatism.

No I have meant field aberrations.

 

Most probably this flattner is two-lens afocal system. It introduces small portion of spherical aberration and corrects astigmatism and curvature keeping the same level of chromatic aberrations. For longer focal length refractor this corrector (in the same position from focal plane) introduces too much astigmatism and curvature compensation (overcorrection) and it is recommended to move it a bit closer to focal plane making optimal astigmatism and curvature correction. But aberration balance becomes different and their correction is broken. Mostly and an issue is coma.

 

So the flattner works fine (excluding small portion of spherical aberration) in quite narrow range of focal length.

The TSFlat 2" is a two element system that seems to work well for a 600mm focal length. I would have to test for spherical aberration at higher magnification, not at 15x. Then again, there is no need to use the flattener at 30-50x/inch. I might be able to reduce the edge astigmatism a bit by changing the spacing, but I suspect not by much. Playing with the spacing also defeats a certain "plug and play" quality of this thing. What I like is the ability to focus the field without eye strain.

[YKSE]

 

When Ernest mentions over, or under-correction, I think he is mentioning spherical aberration, and that isn't an issue here. I am getting edge astigmatism.

 

No I have meant field aberrations.

 

Most probably this flattner is two-lens afocal system. It introduces small portion of spherical aberration and corrects astigmatism and curvature keeping the same level of chromatic aberrations. For longer focal length refractor this corrector (in the same position from focal plane) introduces too much astigmatism and curvature compensation (overcorrection) and it is recommended to move it a bit closer to focal plane making optimal astigmatism and curvature correction. But aberration balance becomes different and their correction is broken. Mostly and an issue is coma.

 

So the flattner works fine (excluding small portion of spherical aberration) in quite narrow range of focal length.

 

By the way, note that...

- three lens flattner corrects field aberrations without introducing even a sign of spherical aberration

- both type afocal flattners are quite sensitive to distance from focal plane

 

Very informative, Ernest.

 

The amount of spherical aberration introduced by this two lens flattener, is it mostly over-correction or under-correction?

Do many refractors have slightly over-correction or under-correction too? if so, can this flattener actually make better correction of the system if the corrections happen to be opposite?

[Piotr K.]

The Diagonal is a GSO 2" Dielectric. I measured the light path of this diagonal to be 113mm....a lucky number as it happens!
(...)
Photo's of the scopes in question and the FF on the diagonal.

Hi Messyone, and hi all other guys! I found this topic and it is very interesting for me, because I also like WF observations I have several refractors (SW 80/400, 120/600, 150/750, SW Equinox 120/900), normal (=not dielectric) GSO 2" diagonal, and I have just bought TSFlat2 field flattener (on it's way to me at the moment).

I think there might be one mistake done by Messyone, which might be the reason for vignetting and FF not working for all eyepieces tested.

You see, the optical path length of the GSO 2" mirror diagonals seems indeed to be 113 mm - I measured it using the scale on the long drawtube of Baader focuser, which is installed in my Equinox 120/900.

BUT - this optical path begins at the diagonal's wall which is facing the opening of the focuser. NOT where the silver tube of the diagonal ends (I mean, not at the end which is facing the objective of the scope).

The whole silver tube goes inside the focuser, and so, it shouldn't be considered in the light path's lenght. I mean, when you guys screw the FF into the 2" filter thread at the end of the silver tube, you add about 40 mm to the distance between the eyepiece and the FF. So you end up with 113+40=143 mm distance, not with the 113 mm required for Messyone's scope. Not mentioning that the FF is much further away from the eyepiece than recommended by the manufacturer, so I'm not surprised that you observe vignetting.

In my opinion, to achieve the correct distance of 113 mm, you should remove the silver tube from the diagonal, and screw the FF directly into diagonal's wall. Which is not possible without an additional adapter, because the 2" filter thread and GSO 2" diagonal silver tube's thread (at the end which is facing the diagonal's wall) are different.

Please correct me if I'm wrong (and also, please excuse, and help me to correct any possible mistakes in my English - I'm not a native English speaker ).

Edited by Piotr K., 06 October 2017 - 03:31 PM.

[Messyone]

Hi Pitor K,

 

Thanks for your post....very interesting. I have no idea how to measure the light path in a diagonal other than measuring the difference between straight through and then using the diagonal.

 

Anyone who knows any other way, I'd like to know.

 

As luck has it I do have another diagonal with the correct adaptor SCT-m48 so can screw the TSFF onto the diagonal in place of the barrel. Will take a photo soon, with measurements soon.

 

Next clear night I'll be out with this combo and see what happens. 

 

Your English is excellent 

 

Matt

[Peter Besenbruch]

At a focal length of 600mm, you screw the flattener into the end of the nose-piece of the GSO diagonal. Yes, the flattener extends quite a ways into the focuser. I do not know how critical the spacings need to be, but I suspect the distance from field stop to flattener is somewhat important.

[Messyone]

I tried the FF in the two positions on the end of the diagonal barrel and screwed onto an adaptor so the FF became the barrel. 

 

My result in the 80x600 Refractor is the same as before...screwed on the diagonal barrel is the better view, so I'd say that is the way it was designed to be used.

 

The other way, remove barrel and screwed onto the adaptor, has stars looking like coma in a reflector from 70% out.

 

I only tried the 80mm with a Pan 35.

 

Matt

[hersey0308]

Hi Matt - I've watched this thread with interest because I bought the TS FF earlier this summer for the same reason. I had it into a 70ED using the diagonal and noticed a definite improvement in clarity. The star colour was quite improved and so was the field though there was flaring starting at about 70% towards the edge. This was some time ago so I'm working from memory, I had a 2" 32MM Olivion eyepiece (68 degree).

 

 

The F6 70mm is tied up at the moment on another project so I was going to try the F6 AT1010 80mm achro and I'm expecting a good result. Also I found a 14MM extension from a Hyperion eyepiece that fits so I'll see if extending it deeper into the tube makes any difference. Fun though.

 

 

David

Edited by hersey0308, 12 October 2017 - 07:43 PM.