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TS 2" Field Flattener for Visual

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#51 213Cobra

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Posted 01 August 2019 - 01:09 AM

Tried mine last night with 80mm F6, and it did remove a good bit of FC in the 21 Ethos. 

 

Saw some astigmatism at the edge, and I wonder if the flattener is adding that, or if it is just a matter of optimizing the distances.

I use the TSFlat2 on my 80mm f/6 and 80mm f/7.5. The rest of my scopes are intrinsically flat field.  I have tried it with other scopes down to f/4.3. It is spec'd to be effective f/4 - f/9 and I have no reason to question that range as it corresponds with my own experience. TS offers a detailed grid of working distances relative to telescope focal length and they note that for visual, there is at least 5% error tolerance. This is also consistent with my experiences. Mike found that when he reduced the working distance by screwing the TSFlat2 into the diag in place of the nosepiece rather than as an extension to the nosepiece, it cleaned up his ST120, after initially having a negative reaction on that scope. The working distance matters! But you have some latitude.

 

I have not seen any astigmatism induced by the TSFlat2 on an 80/480, but then I use eyepieces that are not astigmatic, and I use DiopTrx to tune out my eye's astigmatism at exit pupils above 1mm. Anyway, before you draw definitive conclusions about the flattener, do what you can to optimize working distance within the 5% visual tolerance for error.

 

Phil


Edited by 213Cobra, 01 August 2019 - 08:58 AM.

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#52 areyoukiddingme

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Posted 12 August 2019 - 01:04 PM

Thanks, I'll look up the table . . . 

 

As it happens, I messed with distance a little the other night. Used it with the 31 Nagler in the 80/480, and found that the quality of the correction improved by pulling the eyepiece out further (maybe a 1/4 inch). Pulling out further still made it worse.

 

So the only issue there would be figuring out how to get good correction for a few different eyepieces. But that shouldn't be a huge issue, as I only want to correct low power, and possibly 1 or 2 medium low eyepieces.

 

The best view I got was with the Nikon 17 HW at a dark site. It wasn't quite as good as my Televue 101, but it was very good indeed.


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#53 213Cobra

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Posted 12 August 2019 - 05:55 PM

Thanks, I'll look up the table . . . 

 

As it happens, I messed with distance a little the other night. Used it with the 31 Nagler in the 80/480, and found that the quality of the correction improved by pulling the eyepiece out further (maybe a 1/4 inch). Pulling out further still made it worse.

 

So the only issue there would be figuring out how to get good correction for a few different eyepieces. But that shouldn't be a huge issue, as I only want to correct low power, and possibly 1 or 2 medium low eyepieces.

 

The best view I got was with the Nikon 17 HW at a dark site. It wasn't quite as good as my Televue 101, but it was very good indeed.

In principle this rule applies: the shorter the refractor´s focal length, the longer the working distance to the sensor has to be.

♦ 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

5% tolerance with no effects.



#54 howardcano

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Posted 04 May 2020 - 11:08 AM

I want to thank everyone here for your experimentation with the TSFLAT2 for visual.  I recently bought one used from the CN classifieds, and did a quick check last night with my 102mm f/7 refractor.  While the optimum position for the TSFLAT2 would be within the barrel of the diagonal, I don't trust my shaky hands to try removing the field flattener elements from their housing and modifying the diagonal to accept them, so I simply screwed the housing to the end of the diagonal.

 

The result was a substantial reduction in field curvature, to the point where the view at the edge of my ES 40mm 68degree eyepiece was dominated by residual astigmatism and a touch of coma.  My Panoptic 35mm was better, due to the smaller field and (probably) better design.

 

I didn't have time to compare the Panoptic to my ES 34mm 68degree (though I know the Pan is somewhat better in my 200mm f/6 Newtonian).  That will have to wait for another night.


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#55 howardcano

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Posted 16 June 2020 - 12:06 PM

Here's an update for using the TSFLAT2 field flattener with GSO 2" diagonals:

This adapter permits the TSFLAT2 to screw directly into the GSO diagonal body when the diagonal barrel is removed:

 

Baader 2" Ext / M48i Zero-length Reducing Piece (Zero Optical Length) # M48-2 2454834

https://agenaastro.c...-2-2454834.html

 

If more spacing is needed between the eyepiece focal plane and the TSFLAT2, use an M48 spacer of the appropriate length, similar to this:

 

Blue Fireball 2" Spacer Ring with 0.75" Extension # S-2C

https://agenaastro.c...-extension.html


Edited by howardcano, 16 June 2020 - 12:07 PM.

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#56 Jon Isaacs

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Posted 31 October 2020 - 11:18 PM

I use the TSFlat2 on my 80mm f/6 and 80mm f/7.5. The rest of my scopes are intrinsically flat field.  I have tried it with other scopes down to f/4.3. It is spec'd to be effective f/4 - f/9 and I have no reason to question that range as it corresponds with my own experience. TS offers a detailed grid of working distances relative to telescope focal length and they note that for visual, there is at least 5% error tolerance. This is also consistent with my experiences. Mike found that when he reduced the working distance by screwing the TSFlat2 into the diag in place of the nosepiece rather than as an extension to the nosepiece, it cleaned up his ST120, after initially having a negative reaction on that scope. The working distance matters! But you have some latitude.

 

I have not seen any astigmatism induced by the TSFlat2 on an 80/480, but then I use eyepieces that are not astigmatic, and I use DiopTrx to tune out my eye's astigmatism at exit pupils above 1mm. Anyway, before you draw definitive conclusions about the flattener, do what you can to optimize working distance within the 5% visual tolerance for error.

 

Phil

 

To resurrect this thread:

 

How are you achieving the spacing in a refractor with a 2 inch diagonal?  Are you using eyepieces with 40 mm field stops?

 

Jon



#57 213Cobra

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Posted 02 November 2020 - 04:44 AM

To resurrect this thread:

 

How are you achieving the spacing in a refractor with a 2 inch diagonal?  Are you using eyepieces with 40 mm field stops?

 

Jon

No, seldom; and I'm not concerned about any vignetting. I see very little to none most of the time. -Phil


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#58 Jon Isaacs

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Posted 02 November 2020 - 05:07 AM

No, seldom; and I'm not concerned about any vignetting. I see very little to none most of the time. -Phil

Phil:

 

Thanks for the reply. 

 

I recently acquired a TS Flat2 and based on what I had read here, I was expecting well corrected fields of view in my 80mm F/6 with eyepieces like the 31mm Nagler.  It's the eyepieces with the largest field stops that present the largest amount of field curvature.  I calculate about 1.3 mm for this combination.

 

But I realized that to space the TSFLAT 2 properly, I need to get a new diagonal because while the insertion length of TeleVue Everbrite measured at exactly 4.00 inches (101.6mm), the nose piece adds about 35 mm so minimum spacing possible is 137mm.  The 31mm Nagler adds 9.6mm to this so the actual spacing would be about 147mm minimum.  The spec for a 480mm focal length is about 120mm. 

 

The 35mm Panoptic is better spaced, it's gives 4mm so it would be spaced at 133mm.  But from what I saw with the spacings above, the view was not at all clean by my standards and I was seeing a combination of astigmatism and field curvature, something I don't see with either eyepiece in my NP-101.  

 

I have decided that what I need to properly space the TSFLAT2 is a 2 inch diagonal with a removable nosepiece with the standard threads used for 2 inch accessories.  That way, the TSFlat2 can serve as the nosepiece.  I think I read in this thread that the GSO Diagonal has the feature.    

 

That's why I wondered how you were spacing your TSFLAT 2 and whether you were using eyepieces like the 31mm Nagler that pushed the limits.  

 

Jon


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#59 Piotr K.

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Posted 02 November 2020 - 05:38 AM

> That's why I wondered how you were spacing
> your TSFLAT 2 and whether you were using
> eyepieces like the 31mm Nagler that pushed
> the limits.

I tested TSFLAT2 with Nagler 31, Ethos 21 and Maxvision 20 and 28 eyepieces, using 80/400 f/5 refractor. I also did a lot to keep the proper distance between the flattener and the fieldstop of the eyepieces. I used several rings of 2” filters as 5mm „spacers”, screwing the flattener instead of the nosepiece into the wall of the mirror diagonal (don’t remember at the moment what diagonal it was - GSO or Explore Scientific 2”). So I used the flattener as a nosepiece. On the eyepiece side, when sliding the eyepiece up and down in the 2” socket of the diagonal I was able to set almost exact distance, required for 400 mm focal lenght.

And my conclusion is one and definite - it doesn’t work for visual use.

The stars were looking worse than without the flattener, and in no way were they „pinpoint from edge to edge”. And I’m pretty sure the flattener itself was functioning OK, because I tested it in astrophotography, and it did reduce the field curvature.
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#60 Jon Isaacs

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Posted 02 November 2020 - 06:07 AM

And my conclusion is one and definite - it doesn’t work for visual use.

 

The stars were looking worse than without the flattener, and in no way were they „pinpoint from edge to edge”. And I’m pretty sure the flattener itself was functioning OK, because I tested it in astrophotography, and it did reduce the field curvature.

 

Piotr:

 

Thanks for sharing your experiences.  I may be able to borrow a GSO or ES diagonal, in which case I will give it a try. 

 

I am also thinking I will try it in my NP-101 just to see what it does to a scope already corrected for field curvature.  It could be interesting.

 

Jon



#61 213Cobra

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Posted 02 November 2020 - 06:49 AM

Phil:

 

Thanks for the reply. 

 

I recently acquired a TS Flat2 and based on what I had read here, I was expecting well corrected fields of view in my 80mm F/6 with eyepieces like the 31mm Nagler.  It's the eyepieces with the largest field stops that present the largest amount of field curvature.  I calculate about 1.3 mm for this combination.

 

But I realized that to space the TSFLAT 2 properly, I need to get a new diagonal because while the insertion length of TeleVue Everbrite measured at exactly 4.00 inches (101.6mm), the nose piece adds about 35 mm so minimum spacing possible is 137mm.  The 31mm Nagler adds 9.6mm to this so the actual spacing would be about 147mm minimum.  The spec for a 480mm focal length is about 120mm. 

 

The 35mm Panoptic is better spaced, it's gives 4mm so it would be spaced at 133mm.  But from what I saw with the spacings above, the view was not at all clean by my standards and I was seeing a combination of astigmatism and field curvature, something I don't see with either eyepiece in my NP-101.  

 

I have decided that what I need to properly space the TSFLAT2 is a 2 inch diagonal with a removable nosepiece with the standard threads used for 2 inch accessories.  That way, the TSFlat2 can serve as the nosepiece.  I think I read in this thread that the GSO Diagonal has the feature.    

 

That's why I wondered how you were spacing your TSFLAT 2 and whether you were using eyepieces like the 31mm Nagler that pushed the limits.  

 

Jon

Yes, I use the TSFLat2 as the nosepiece on 2" diagonals with my 80/480 f/6 LOMO and my 80/600 f/7.5 LOMO. My other scopes are all flat field quads (or an Epsilon hyperbolic astrograph Newtonian I use visually). I barely need the TSFlat2 with the f/7.5 LOMO but it makes a clear difference on the f/6 scope. You have *at least* 5% leeway visually on the spacing. I successfully use 22mm Panoptic, 31mm Nagler, 32mm Tak Erfle and 41mm Panoptic with TSFlat2 with clean visuals. The least clean visual in this config is the 31mm Baader Aspheric but it has other merits in other scopes.

 

The GSO dielectric can take the TSFlat as a nosepiece, as can the Stellarvue 2" diag. I've also used it with a Lumicon 2". For no particular reason I haven't tried to screw the TSFlat into my AP Maxbright, but I can try that tomorrow and let you know.

 

Phil


Edited by 213Cobra, 02 November 2020 - 07:37 PM.

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#62 Sarkikos

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Posted 02 November 2020 - 08:21 AM

 

I have decided that what I need to properly space the TSFLAT2 is a 2 inch diagonal with a removable nosepiece with the standard threads used for 2 inch accessories.  That way, the TSFlat2 can serve as the nosepiece.  I think I read in this thread that the GSO Diagonal has the feature.    

Or you can get a 2" diagonal with SCT threads.  Attach an SCT-48mm ring adapter to the diagonal, and then screw on the TSFLAT2.

 

Mike


Edited by Sarkikos, 02 November 2020 - 08:21 AM.


#63 howardcano

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Posted 02 November 2020 - 08:42 AM

I'm using the TSFLAT2 on two scopes: a 102mm F/7, and a 72mm F/6 (approximately, as I'm not using all of the aperture); and with ES40/68 and a Panoptic 35 eyepieces.  In both cases the spacing needed to be significantly larger than the spec.  I'm guessing that the extra correction was needed to cancel out field curvature in the eyepieces.

 

The smaller scope has the TSFLAT2 screwed directly into the end of the stock GSO diagonal, and the longer scope has perhaps 10 to 15mm less spacing, using the parts I mentioned above.

 

The ES40/68 still shows some aberrations at the field edges in 102mm F/7, but best focus position is the same across the field.  The Panoptic 35 looks very good in both scopes.  Again, I'm guessing that the Panoptic is simply better corrected than the ES.



#64 howardcano

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Posted 02 November 2020 - 08:45 AM

I have decided that what I need to properly space the TSFLAT2 is a 2 inch diagonal with a removable nosepiece with the standard threads used for 2 inch accessories.  That way, the TSFlat2 can serve as the nosepiece.  I think I read in this thread that the GSO Diagonal has the feature.    

The GSO diagonal needs the "Baader 2" Ext / M48i Zero-length Reducing Piece (Zero Optical Length) # M48-2 2454834" to adapt the diagonal body to the 48mm threads on the TSFLAT2.  It's a bit pricey, but they probably don't sell too many.


Edited by howardcano, 02 November 2020 - 08:46 AM.


#65 Jon Isaacs

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Posted 02 November 2020 - 06:43 PM

Yes, I use the TSFLat2 as the nosepiece on 2" diagonals with my 80/480 f/6 LOMO and my 80/600 f/7.5 LOMO. My other scopes are all flat field quads (or an Epsilon hyperbolic astrograph Newtonian I use visually). I barely need the TSFlat2 with the f/7.5 LOMO but it makes a clear difference on the f/6 scope. You have *at least* 5% leeway visually on the spacing. I successfully use 22mm Panoptic, 31mm Nagler, 32mm Tak Erfle and 41mm Panoptic with TSFlat2 with clean visuals. The least clean visual in this config is the 31mm Baader Aspheric but it has other merits in other scopes.

 

The GSO dielectric can take the TSFlat as a nosepiece, as can the Stellarvue 2" diag. I've also used it with a Lumicon 2". For no particular reason I haven't tried to screw the TSFlat into my AP Maxbright, but I can try that tomorrow and let you know.

 

Phil

 

Phil

 

Phil:

 

I was able to borrow a friend's William Optics diagonal and the TSFLAT2 does screw in as a nosepiece so I'll be able to try it myself this evening.

 

Thank you to everyone contributing to this thread.. 

 

Jon



#66 Jon Isaacs

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Posted 03 November 2020 - 12:43 PM

Phil:

 

I was able to borrow a friend's William Optics diagonal and the TSFLAT2 does screw in as a nosepiece so I'll be able to try it myself this evening.

 

Thank you to everyone contributing to this thread.. 

 

Jon

 

 

Just an update:

 

With the TSFlat2 screwed directly to the WO diagonal, it seemed much better.  My backyard skies are bright so I won't really know how sharp it will be under dark skies but with the 31mm Nagler, 21 mm, 13mm and 8 mm Ethos, I thought everything seemed quite sharp across the field in my Astro-Tech 80 mm F/6 AT-80 LE.  

 

Bright stars like Altair seemed quite sharp even at the edge of 31 mm.

 

Jon


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#67 tony_spina

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Posted 03 November 2020 - 01:14 PM

Jon,

Did you order the TSFLAT2 from TS?  I ordered one last year and it didn't work for me. All the stars showed astigmatism.  Was able to return back to Germany,  but it was a hassle 

 

If some vendor in the US carries it I would liket to try again to use with my ST120 



#68 Jon Isaacs

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Posted 03 November 2020 - 04:40 PM

Jon,

Did you order the TSFLAT2 from TS?  I ordered one last year and it didn't work for me. All the stars showed astigmatism.  Was able to return back to Germany,  but it was a hassle 

 

If some vendor in the US carries it I would liket to try again to use with my ST120 

 

I bought it second hand from Jeff Morgan..

 

Piotr's post to this thread was what made me realize I'd made a mistake in my calculations.

 

https://www.cloudyni...sual/?p=8143252

 

 

"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."

 

I had measured the Everbrite at 101.6 mm but had forgotten to include the nose piece.  

 

A light went on in my head when unread Piotr's post.

 

Jon



#69 Sarkikos

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Posted 04 November 2020 - 06:55 AM

I'm using the TSFLAT2 on two scopes: a 102mm F/7, and a 72mm F/6 (approximately, as I'm not using all of the aperture); and with ES40/68 and a Panoptic 35 eyepieces.  In both cases the spacing needed to be significantly larger than the spec.  I'm guessing that the extra correction was needed to cancel out field curvature in the eyepieces.

 

The smaller scope has the TSFLAT2 screwed directly into the end of the stock GSO diagonal, and the longer scope has perhaps 10 to 15mm less spacing, using the parts I mentioned above.

 

The ES40/68 still shows some aberrations at the field edges in 102mm F/7, but best focus position is the same across the field.  The Panoptic 35 looks very good in both scopes.  Again, I'm guessing that the Panoptic is simply better corrected than the ES.

AFAIK, the only aberration the TSFLAT2 will correct is field curvature.  If an aberration at field edge can be corrected by adjusting the focuser, it's probably field curvature.  Otherwise, it's probably astigmatism from the eyepiece.

 

Mike


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#70 howardcano

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Posted 05 November 2020 - 09:09 PM

AFAIK, the only aberration the TSFLAT2 will correct is field curvature.  If an aberration at field edge can be corrected by adjusting the focuser, it's probably field curvature.  Otherwise, it's probably astigmatism from the eyepiece.

 

Mike

Yes, I'm pretty sure what remains is astigmatism in the ES40/68.  I also see it in the ES34/68, while the Panoptic 35 shows none.  But I'm also pretty sure that the extra spacing also eliminates field curvature present in all of these eyepieces.  Don Pensack has stated he has seen field curvature in the Panoptic 35, and I agree.  It's not much, but I can still find it with my zero-accommodation eyeballs.  Fortunately, the TSFLAT2 fixes it.


Edited by howardcano, 05 November 2020 - 09:12 PM.


#71 213Cobra

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Posted 07 November 2020 - 04:56 AM

AFAIK, the only aberration the TSFLAT2 will correct is field curvature.  If an aberration at field edge can be corrected by adjusting the focuser, it's probably field curvature.  Otherwise, it's probably astigmatism from the eyepiece.

 

Mike

Correct. Only FC is corrected. But for visual if you at least approximate the distancing per guidelines from TS within ~ 5%, it will prove effective for what it is supposed to do but not for what is outside its design mandate.

 

Phil



#72 Jon Isaacs

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Posted 07 November 2020 - 08:55 AM

Yes, I'm pretty sure what remains is astigmatism in the ES40/68.  I also see it in the ES34/68, while the Panoptic 35 shows none.  But I'm also pretty sure that the extra spacing also eliminates field curvature present in all of these eyepieces.  Don Pensack has stated he has seen field curvature in the Panoptic 35, and I agree.  It's not much, but I can still find it with my zero-accommodation eyeballs.  Fortunately, the TSFLAT2 fixes it.

 

I don't see field curvature using the 35 mm Panoptic in my NP-101.. I'll give it a try again using a bright star to double check.

 

My eyes qualify as low accommodation,  I use readers from 1.0 diopters to 4.0 diopters plus an optiVISOR for soldering and close work and would use 0.75s and maybe 0.5s if they made them.. :)

 

Jon

 

Jon



#73 25585

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Posted 07 November 2020 - 11:57 AM

I don't see field curvature using the 35 mm Panoptic in my NP-101.. I'll give it a try again using a bright star to double check.

 

My eyes qualify as low accommodation,  I use readers from 1.0 diopters to 4.0 diopters plus an optiVISOR for soldering and close work and would use 0.75s and maybe 0.5s if they made them.

 

You can get Dioptrx in low strengths. Just needs a frame.



#74 Jon Isaacs

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Posted 08 November 2020 - 09:38 AM

You can get Dioptrx in low strengths. Just needs a frame.

 

I don't need a dioptrix, I don't have astigmatism, I have presbyopia,  very little accommodation,  my eyes are basically focused at infinity. I need help closeup. 

 

0.5 readers would help me focus at around 6 feet, about right for seeing the TuBlug with my big scope.

 

Jon



#75 André Pira

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Posted 08 November 2020 - 05:10 PM

Good evening everyone! First I apologize for my English, I am using the google translator. I have read all the posts and would like to know the reference point for measuring the ideal working distance of the flattener?
Is it the upper lens of the eyepiece, where the image is formed? Or the beginning of the eyepiece barrel?
My telescope is a Takahashi FS 102, so the ideal distance according to the manufacturer's instructions would be 108 mm.


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