44 replies to this topic

[helpwanted]

Hello all, 

 

I just got back from the eye doctor, I am mildly farsighted and need reading glasses, they are not used when viewing through the telescope, but I found out something that I didn't know 2 years ago when I went to the eye doctor. Back then I was found to have astigmatism (I wish they told me!). Today it was measured at .50 for my right eye / observing eye. 

 

So first, I remember seeing incredible detail on Jupiter from a 4" APO about 8 years ago at only 100x, even better above that, but now on nights that I think the seeing is good, and ClearSky Clock also says it's good, I feel like the detail is maxed out at 133x, and even that is not a great as my memory from years ago. Now I know my memory from years ago could be wrong or exaggerated, but I still feel like I am not seeing the best detail anymore when looking at Jupiter (just one example), and not able to go very high in magnification. 

 

Is what I am describing the result of the astigmatism? Is that seen at all magnifications, or only at high magnifications? I know what astigmatism should look like when looking at star tests articles, but I don't see that when looking through the scope. Could it not be noticeable yet still be degrading my details? 

 

I use Delos eyepieces and a 24pano, all can use the Dioptrx (the 24pano needs an adapter), will I see a noticeable increase in detail at any and all magnifications? 

Will I loose anything by using them?

 

As for my scopes, too many to admit to, but for comparison with the 4" APO from years ago, I have a FC100-DZ now. 

 

Any input is greatly appreciated!

 

Thank you,

David

 

[Michael Covington]

Could well be.  The most obvious sign of astigmatism is that stars out of focus are elliptical, and on the other side of focus, they are elliptical in a perpendicular direction.   Install the DioptRx and rotate it to make the slightly-out-of-focus stars round, then focus precisely, and they'll be sharper than before.

I put a small piece of white paper tape on the edge of my DioptRx to help me quickly rotate it into the usual position every time.  I placed it where it would be straight up relative to my head.

[helpwanted]

The most obvious sign of astigmatism is that stars out of focus are elliptical, and on the other side of focus, they are elliptical in a perpendicular direction.

 

But that I do not see, at any magnification. That’s what’s making this hard for me to figure out if it’s affecting the view

[dnichols]

I have been asking myself similar questions lately.  According to Televue 0.50 astigmatism with an f8 scope should only be a problem with eyepieces 32mm or larger.

 

https://www.televue....=54&Tab=_Choose

[helpwanted]

I have been asking myself similar questions lately.  According to Televue 0.50 astigmatism with an f8 scope should only be a problem with eyepieces 32mm or larger.

 

https://www.televue....=54&Tab=_Choose

I saw that on their website. It truly could just be really bad seeing conditions for me locally, I guess I’m hoping that one of these will be a magic solution. 

[Michael Covington]

I have been asking myself similar questions lately.  According to Televue 0.50 astigmatism with an f8 scope should only be a problem with eyepieces 32mm or larger.

 

https://www.televue....=54&Tab=_Choose

I have 0.50 astigmatism and can definitely see it with a 2-mm exit pupil even though their chart says it shouldn't be a problem.

[Starman1]

Hello all, 

 

I just got back from the eye doctor, I am mildly farsighted and need reading glasses, they are not used when viewing through the telescope, but I found out something that I didn't know 2 years ago when I went to the eye doctor. Back then I was found to have astigmatism (I wish they told me!). Today it was measured at .50 for my right eye / observing eye. 

 

So first, I remember seeing incredible detail on Jupiter from a 4" APO about 8 years ago at only 100x, even better above that, but now on nights that I think the seeing is good, and ClearSky Clock also says it's good, I feel like the detail is maxed out at 133x, and even that is not a great as my memory from years ago. Now I know my memory from years ago could be wrong or exaggerated, but I still feel like I am not seeing the best detail anymore when looking at Jupiter (just one example), and not able to go very high in magnification. 

 

Is what I am describing the result of the astigmatism? Is that seen at all magnifications, or only at high magnifications? I know what astigmatism should look like when looking at star tests articles, but I don't see that when looking through the scope. Could it not be noticeable yet still be degrading my details? 

 

I use Delos eyepieces and a 24pano, all can use the Dioptrx (the 24pano needs an adapter), will I see a noticeable increase in detail at any and all magnifications? 

Will I loose anything by using them?

 

As for my scopes, too many to admit to, but for comparison with the 4" APO from years ago, I have a FC100-DZ now. 

 

Any input is greatly appreciated!

 

Thank you,

David

Astigmatism in the eye is most visible with large exit pupils and disappears with smaller exit pupils.

I need glasses when the exit pupil exceeds 1.5mm, but take them off (they make no visible difference) when the exit pupils are smaller.

So if you see bad images at high power, but not at low power, it is one of the 3 "C"s:

1) lack of cooling of the optics.  Until the scope reaches the temperature of the air, there is a warm boundary layer in front of the optics that blurs the image.

2) poor collimation.  Tolerances for collimation get tighter at higher powers.

3) poor conditions.  Bad seeing because the air is not steady, or a high altitude haze that smears fine detail in the eyepiece.

 

100x is a 1mm exit pupil in a 4" scope, so the issue is not astigmatism (though it is always possible there might be some in the optics), but one of the above.

Given it is a 4" refractor, it is almost surely #3.  So try to observe every night so you can catch better seeing when it occurs.  Once you see a clean sharp image in the scope, even once,

you know from that point forward it is not in the eye or the scope when the image is blurrier.

 

If it's been more than 2 years since your last eye exam, I would address that, too.

[russell23]

The most obvious sign of astigmatism is that stars out of focus are elliptical, and on the other side of focus, they are elliptical in a perpendicular direction.

 

But that I do not see, at any magnification. That’s what’s making this hard for me to figure out if it’s affecting the view

0.5 diopters of astigmatism is not too bad.  At 133x with a 4” scope the exit pupil is much smaller than the size needed to see the effects of your astigmatism.  I have 1.75 diopters in my observing eye and can observe without astigmatism correction at 133x if I choose to. At 100x or less I always wear my glasses to correct the astigmatism.

[helpwanted]

Thank you all, glad to hear it looks like it's not my eyes! I have to agree with you Don about #3, the Phoenix metro area is known for dark and dry skies, but not necessarily good seeing. Maybe that night years ago was the exception for me. I can't really test anything for a while, summer in Phoenix is either monsoon rains or nights with temps in the 100s all night long. As soon as the summer heat breaks I will back out every night and get a better idea of what's going on. 

 

Oh and I went to eye doctors yesterday, so now I am up to date... two years since the last one though!

 

 

 

So back to .50, should I be using a Dioptrx with my 24pano? while only 3mm exit pupil on this APO, I'm above 4mm on my Dob & Mak-Newt. 

[davidgmd]

 

So back to .50, should I be using a Dioptrx with my 24pano? while only 3mm exit pupil on this APO, I'm above 4mm on my Dob & Mak-Newt. 

    
You mentioned in your OP that you wear reading glasses. Are they over the counter or prescription? If prescription, and if they contain the astigmatism correction, you can try comparing the sharpness of the view with and without the glasses. Use the focuser to tune out the non-astigmatic portion of the correction.
 
If you see better with certain eyepieces when the astigmatism-correcting glasses are on, those are the eyepieces that will benefit from a Dioptrx. If the glasses make no difference, a Dioptrx probably won’t either.

[cimar]

I use 1.5ish Dioptrxs and these are a blessing for me.

To correct 0.5 diopters of cylinder seems less significant.

[helpwanted]

    
You mentioned in your OP that you wear reading glasses. Are they over the counter or prescription? If prescription, and if they contain the astigmatism correction, you can try comparing the sharpness of the view with and without the glasses. Use the focuser to tune out the non-astigmatic portion of the correction.
 
If you see better with certain eyepieces when the astigmatism-correcting glasses are on, those are the eyepieces that will benefit from a Dioptrx. If the glasses make no difference, a Dioptrx probably won’t either.

great idea, yes to prescription, I will give it a try

[helpwanted]

I use 1.5ish Dioptrxs and these are a blessing for me.

To correct 0.5 diopters of cylinder seems less significant.

yeah I need to do some testing before I buy! 

[Starman1]

Thank you all, glad to hear it looks like it's not my eyes! I have to agree with you Don about #3, the Phoenix metro area is known for dark and dry skies, but not necessarily good seeing. Maybe that night years ago was the exception for me. I can't really test anything for a while, summer in Phoenix is either monsoon rains or nights with temps in the 100s all night long. As soon as the summer heat breaks I will back out every night and get a better idea of what's going on. 

 

Oh and I went to eye doctors yesterday, so now I am up to date... two years since the last one though!

 

 

 

So back to .50, should I be using a Dioptrx with my 24pano? while only 3mm exit pupil on this APO, I'm above 4mm on my Dob & Mak-Newt. 

With 0.5 diopters of astigmatism, it is likely you would see some improvement in the stars at a 3mm exit pupil and definitely above 4mm.

 

My own eye has 1.0 diopter of astigmatism, and an experiment showed I could see an improvement in the in-focus star images down to a 1.5mm exit pupil with corrective glasses.

And, it also showed I could detect out of focus astigmatism in star images down to a 0.8mm exit pupil, though NOT in focus.

I thought it meant I actually had more astigmatism than 1.0 diopter, but glasses that have exactly that correction turns naked eye stars into tiny round points with no flares, and that is obviously with

my full dark-adapted pupil diameter.

So, there is an exit pupil:

--below which you can see no evidence of astigmatism in or out of focus

--below which you can see no evidence of astigmatism in focus

The TeleVue chart on their DioptRx page shows a fairly liberal interpretation of the latter.  it applies if you are not particularly fussy about in-focus star images.

A few notes about the DioptRx:

• the correction, appropriately-chosen, will be better than glasses, and with less reflection because of astronomy-level anti-reflection coatings.
• they sacrifice at least 8mm of eye relief, and maybe more if the top lens is concave.  You have to be willing to use very short eye reliefs if installed on an eyepiece with less than 17-18mm of eye relief.
• they require rotation every time the eyepiece changes angle, as happens in a dob.
• unless you have several of them, you will be transferring the DioptRx from eyepiece to eyepiece frequently.
• they don't help you read your notes or see stars in the sky well or help you use any form of red dot finder with full pupil diameter
• they make sharing the view with others difficult/unlikely.

But, there are a number of side issues with glasses as well:

• you may see internal reflections in the glasses lenses on very bright objects.  Anti-reflection coatings are never up to astronomy standards.
• you may need even more eye relief to accommodate glasses than to accommodate a DioptRx.
• you won't see sharp images across the field with progressives, and bifocals may have the lower section in the field, so single vision glasses are the way to go, but may require changing glasses to read notes.
• you may have to get all new eyepieces if your current ones don't accommodate glasses.
• yet, if you focus your scope wearing glasses, other people will find the focus pretty good already when they look through, especially others who wear glasses.
• and glasses help prevent fogging of the eyepieces
• and glasses don't need rotation with angle change on the eyepieces, so you can tilt your head and still see the same image sharpness.
• and glasses can also correct refractive error as well so you can avoid the optical issues associated with refocusing--an issue especially relevant for coma correction.

 

So, some pluses and minuses to each.

[helpwanted]

With 0.5 diopters of astigmatism, it is likely you would see some improvement in the stars at a 3mm exit pupil and definitely above 4mm.

 

My own eye has 1.0 diopter of astigmatism, and an experiment showed I could see an improvement in the in-focus star images down to a 1.5mm exit pupil with corrective glasses.

And, it also showed I could detect out of focus astigmatism in star images down to a 0.8mm exit pupil, though NOT in focus.

I thought it meant I actually had more astigmatism than 1.0 diopter, but glasses that have exactly that correction turns naked eye stars into tiny round points with no flares, and that is obviously with

my full dark-adapted pupil diameter.

So, there is an exit pupil:

--below which you can see no evidence of astigmatism in or out of focus

--below which you can see no evidence of astigmatism in focus

The TeleVue chart on their DioptRx page shows a fairly liberal interpretation of the latter.  it applies if you are not particularly fussy about in-focus star images.

A few notes about the DioptRx:

• the correction, appropriately-chosen, will be better than glasses, and with less reflection because of astronomy-level anti-reflection coatings.
• they sacrifice at least 8mm of eye relief, and maybe more if the top lens is concave.  You have to be willing to use very short eye reliefs if installed on an eyepiece with less than 17-18mm of eye relief.
• they require rotation every time the eyepiece changes angle, as happens in a dob.
• unless you have several of them, you will be transferring the DioptRx from eyepiece to eyepiece frequently.
• they don't help you read your notes or see stars in the sky well or help you use any form of red dot finder with full pupil diameter
• they make sharing the view with others difficult/unlikely.

But, there are a number of side issues with glasses as well:

• you may see internal reflections in the glasses lenses on very bright objects.  Anti-reflection coatings are never up to astronomy standards.
• you may need even more eye relief to accommodate glasses than to accommodate a DioptRx.
• you won't see sharp images across the field with progressives, and bifocals may have the lower section in the field, so single vision glasses are the way to go, but may require changing glasses to read notes.
• you may have to get all new eyepieces if your current ones don't accommodate glasses.
• yet, if you focus your scope wearing glasses, other people will find the focus pretty good already when they look through, especially others who wear glasses.
• and glasses help prevent fogging of the eyepieces
• and glasses don't need rotation with angle change on the eyepieces, so you can tilt your head and still see the same image sharpness.
• and glasses can also correct refractive error as well so you can avoid the optical issues associated with refocusing--an issue especially relevant for coma correction.

 

So, some pluses and minuses to each.

thank you very much for the info!!

[Second Time Around]

To add to Don's very useful pros and cons I use glasses on the rare occasions I view with others.  On my own I prefer a Dioptrx for the following reasons:

 

 

1) I wear my glasses on a cord and have no problems taking them on and off - it becomes automatic

 

2) In any event, I have no presbyopia and so don't need glasses at all for looking at close range objects such as screens or maps

 

3) I have a Dioptrx on my finder eyepiece, but even without this I don't find astigmatism critical on a finder as it's doing just that - finding

 

4) The coatings are better than on even the top of the range Rodenstock lenses on my glasses

 

5) The angle of my astigmatism changes between my annual eye tests.  With a Dioptrx I can adjust this at the telescope

 

6) I find that, like many, I need an extra 0.25 correction for astigmatism at night

 

7) And most of all, having done head to head tests I found that I can see more with a Dioptrx than with my glasses

[Starman1]

To add to Don's very useful pros and cons I use glasses on the rare occasions I view with others.  On my own I prefer a Dioptrx for the following reasons:

 

 

1) I wear my glasses on a cord and have no problems taking them on and off - it becomes automatic

 

2) In any event, I have no presbyopia and so don't need glasses at all for looking at close range objects such as screens or maps

 

3) I have a Dioptrx on my finder eyepiece, but even without this I don't find astigmatism critical on a finder as it's doing just that - finding

 

4) The coatings are better than on even the top of the range Rodenstock lenses on my glasses

 

5) The angle of my astigmatism changes between my annual eye tests.  With a Dioptrx I can adjust this at the telescope

 

6) I find that, like many, I need an extra 0.25 correction for astigmatism at night

 

7) And most of all, having done head to head tests I found that I can see more with a Dioptrx than with my glasses

Steve, your points are very good.  #5 is a reason to dislike the DioptRx (in a dob, the eyepiece angle changes with elevation of pointing), but it is also a reason to love it.

#4 (and #7) is a very good one--the anti-reflection coatings on a DioptRx lens are simply better than any glasses I've ever seen.  Glasses never get astronomy-level AR coatings.

[SteveG]

.  Glasses never get astronomy-level AR coatings.

And are typically made from plastic.

[Second Time Around]

And are typically made from plastic.

And scratch easily!

[Starman81]

I have a question about night time astigmatism and what rating DioptRx is optimal. My presciption has been 3.00 diopters of astigmatism in my observing forever (2.75 in the other I believe) and I have used 3.00 DioptRxs for as long as ever. Would a 3.50 unit (since no 3.25 is available) perform even better in some way? 

[Starman1]

I have a question about night time astigmatism and what rating DioptRx is optimal. My prescription has been 3.00 diopters of astigmatism in my observing forever (2.75 in the other I believe) and I have used 3.00 DioptRxs for as long as ever. Would a 3.50 unit (since no 3.25 is available) perform even better in some way? 

Not necessarily.

You see, a daylight analysis of your astigmatism may reveal less astigmatism than when your pupil is fully dilated.

 

Example: do you see stars with points or spikes when viewing them with the naked eye (don't lie).  Virtually every human sees them that way,

which is why we draw stars with points.

In fact, though, that's an indication of astigmatism.  Stars should appear as tiny little points.  Maybe with a single diffraction ring around the star if it's bright enough.

But without spikes, points, streaks, etc.

 

Now, go out at night wearing your glasses.  Are the stars tiny points. or is there a flare in any direction?

Assuming you have a recent prescription (and if you don't, make an appointment), if you see the stars as tiny points, your astigmatism prescription is fine and a DioptRx that matches it is also fine.

If, on the other hand, you see spikes or flares on the star images, it is likely your dilated pupil yields a larger amount of astigmatism than your glasses correct.

If this is the case, 0.25 to 0.5 diopter stronger correction may be needed.

 

Other than borrowing a set of flippers, I don't know exactly how you would gauge this.  But it is quite common to need a bit stronger correction at night.

[213Cobra]

To add to Don's very useful pros and cons I use glasses on the rare occasions I view with others.  On my own I prefer a Dioptrx for the following reasons:

 

 

1) I wear my glasses on a cord and have no problems taking them on and off - it becomes automatic

 

2) In any event, I have no presbyopia and so don't need glasses at all for looking at close range objects such as screens or maps

 

3) I have a Dioptrx on my finder eyepiece, but even without this I don't find astigmatism critical on a finder as it's doing just that - finding

 

4) The coatings are better than on even the top of the range Rodenstock lenses on my glasses

 

5) The angle of my astigmatism changes between my annual eye tests.  With a Dioptrx I can adjust this at the telescope

 

6) I find that, like many, I need an extra 0.25 correction for astigmatism at night

 

7) And most of all, having done head to head tests I found that I can see more with a Dioptrx than with my glasses

My extended experience with DioptRx is the same. Better than glasses, nothing currently-available beats it. I buy one for every eyepiece longer than 10mm FL.  -Phil

[TayM57]

The dioptrx for me, proved to be impractical for use in the field. I did not like having to take my glasses on/off. Glasses for telrad, off for EP. Ditto for walking around to swap EPs. Glasses on.

 

The on/off routine with the glasses was becoming impractical, and the cost of outfitting each EP with a dioptrx would be prohibitive. It also makes my hovering style of observing more difficult.

 

However, I think it is fantastic that TV offers the dioptrx as an option for amateur astronomers. If it works for some, great. It just doesn't for me. It's too bad TV can't design a lower profile dioptrx but doing so would mean no twist-lock compression ring.

[russell23]

I think glasses are a great option if you have a pair dedicated to astronomy. My daily wear eyeglasses are progressives so I do not use those for astronomy.  Instead, I also purchased a pair of single vision that I only use for astronomy.  Over the years, the only time glasses have ever given a worse view than without glasses is at higher magnification if the glasses are scratched.  But with a dedicated pair of astronomy glasses scratches are not an issue.

 

Last night I was observing Saturn at 208x with my AT115EDT and the view with glasses was a little sharper than without even though my astigmatism does not require glasses at that exit pupil.  I've compared views with and without glasses and I haven't seen any negative artifacts from my glasses.  I think the key is that you need a dedicated astronomy pair.

 

I tried dioptrx for a few months a couple years ago.  It is very sharp and if you like using it then it is a good option.  The thing I did not like is the extra fiddling when focusing. If the dioptrx is not lined up right when you focus, you spend time adjusting the dioptrx, then the focus and so on until you feel like you found the sharpest image.  With my glasses I just focus.

[SteveG]

I have a question about night time astigmatism and what rating DioptRx is optimal. My presciption has been 3.00 diopters of astigmatism in my observing forever (2.75 in the other I believe) and I have used 3.00 DioptRxs for as long as ever. Would a 3.50 unit (since no 3.25 is available) perform even better in some way? 

Probably not. I’m lucky, and my astigmatism in my viewing eye is only 1.0 to 1.25. I have (2) 1.0 Dioptrx and experimented with a 1.5 Dioptrx. All 3 work perfectly well with no advantages to one or the other. YMMV