Jump to content

sgl_imaging_challenge_2021_annual.thumb.jpg.3fc34f695a81b16210333189a3162ac7.jpg

Help, I'm all at sea with my eyepieces


Aquavit
 Share

Recommended Posts

I can't seem to get comfortable with my eyepieces. I'm a newbie to astronomy (at 64 years old a late arrival) with a MAK 102/1300mm. I quickly ditched the supplied eyepieces and bought a Hyperflex 7.2mm - 21mm zoom along with an Astro Essentials 32mm Plossl and have been observing with these two eyepieces, mainly Lunar but did catch the Jupiter/Saturn conjunction.

The zoom is useful but I find myself staying in the lower mag zone and I can get comfortable with it icy making use of the adjustable cup, I would describe the optical quality as adequate.  The Plossl gives a beautiful crisp image of the Moon with lots of contrast, better optical quality than the zoom but I struggle to get comfortable with it, if I put my eye to the cup I get a barreling effect so the only way to see the whole image is to draw away and this leaves me hovering around above the cup and struggling to stay still. This is the same issue I had with the original included eyepieces, the 10mm being particularly bad.

I'm shortly going to be ordering an 80mm ED frac and, with this in mind and to add to my arsenal of EP's, I ordered a 26mm 62 degree Explore Scientific EP which is a significant upgrade in terms of cost compared to my other EP's. I've just tried this out (in daylight) and the same problem occurs - I can't get close enough to be comfortable.

I'm at a loss to know what the problem is, have I got the wrong eyepieces for my eyes, are they a mismatch with the scope or is it my observing style?

Link to comment
Share on other sites

Some EPs have a twist-up eye cup that you can raise if you don't use specs. Then you can 'rest' part of your face against it to help get the correct position. When I say 'rest' I don't mean lean on it, but it's helpful as a guide for you to keep your eye/face/head in the correct position once you find it.

My Baader, Vixen and BST EPs have this and I find them much easier to use than the OVLs I have with just a rubber eyecup.

 

Link to comment
Share on other sites

Just to reiterate/clarify, following on from what Pixies said, the Plossl and Explore Scientific EP's have fold up/down rubber cups and the zoom has an adjustable eyecup. The zoom  I can get comfortable with and eliminate the barreling, the other two not so.

Link to comment
Share on other sites

To me, it's all to do with eye relief, if you wear spectacles to view then this is more important, but note that the Explore Scientific eyepieces generally have short eye-relief, of the 62° Series only the 20, 26, 32 & 40mm eyepieces have long eye-relief, which means you may struggle with the three shorter focal lengths (5.5, 9 & 14).  It takes a little while to get used to using eyepieces and understanding their various characteristics, but if you have a local astronomy club perhaps you can talk to others and possibly try out their eyepieces?

Edited by rwilkey
  • Thanks 1
Link to comment
Share on other sites

I don't wear specs to view but I was conscious of choosing an EP with reasonable eye relief as I assumed that that was only a good thing. Could the amount of eye relief (ie too much) explain the "barreling" effect I'm experiencing?

Or is it me that needs to get used to viewing through eyepieces???

Link to comment
Share on other sites

6 minutes ago, Aquavit said:

I don't wear specs to view but I was conscious of choosing an EP with reasonable eye relief as I assumed that that was only a good thing. Could the amount of eye relief (ie too much) explain the "barreling" effect I'm experiencing?

Or is it me that needs to get used to viewing through eyepieces???

If by barreling you mean seeing blacks or shadows as you move your head around; then yes, you're inside the exit pupil and are too close to the eye lens of the eyepiece.  There are eyecup extenders or tall eyecups that might help with the 32mm Plossl by giving you a frame of reference for where to keep your eye relative to the eyepiece.

Are sitting while observing?  It's just about impossible to remain still enough while standing to successfully hover above an eyepiece.  There are adjustable observing chairs of all sorts that can help with this.

  • Like 2
  • Thanks 1
Link to comment
Share on other sites

8 minutes ago, Louis D said:

If by barreling you mean seeing blacks or shadows as you move your head around; then yes, you're inside the exit pupil and are too close to the eye lens of the eyepiece.  There are eyecup extenders or tall eyecups that might help with the 32mm Plossl by giving you a frame of reference for where to keep your eye relative to the eyepiece.

Are sitting while observing?  It's just about impossible to remain still enough while standing to successfully hover above an eyepiece.  There are adjustable observing chairs of all sorts that can help with this.

That is what I'm experiencing, I can get a "clear view" if I can hold my eye steady at exactly the right distance but this makes for uncomfortable viewing and is all but impossible to maintain for any length of time. I normally observe standing up but will try sitting down tonight.

Am I right in assuming then that this is a not uncommon phenomena and not a consequence of mis-matched equipment and/or my eyes?

Link to comment
Share on other sites

11 minutes ago, Aquavit said:

Am I right in assuming then that this is a not uncommon phenomena and not a consequence of mis-matched equipment and/or my eyes?

Correct.  It's not like viewing a monitor screen where alignment is irrelevant.  Your eye's entrance pupil has to be exactly aligned with the eyepiece's exit pupil, not only in the left/right and up/down sense, but also the in/out sense as well.  It's a learned skill like riding a bike.  After some time, it just comes naturally and you don't think about it any longer.  That is, until you meet up with an eyepiece with loads of spherical aberration of the exit pupil (SAEP) or kidney beaning.  In this case, it's a fault with the design of the eyepiece that no matter how careful you are, you cannot take in the entire field of view at once.  The best remedy for this is to not buy such an eyepiece in the first place.  That's where the SGL community comes in handy.  We can steer you clear of eyepieces with known design issues such as SAEP.  As far I know, your current eyepieces are not known to have such design issues.

17 minutes ago, Aquavit said:

I normally observe standing up but will try sitting down tonight.

I'm 9 years your junior, and I can't hold myself steady for more than a few minutes before fatigue sets in while standing and observing.  You need to be relaxed and comfortable to get the most out of astronomical observing.

  • Like 3
Link to comment
Share on other sites

Yes, it is the long eye relief on the eyepieces that is causing you a problem.

First, observe seated.  You can hold your head steady much more easily.

Second, perhaps look for eyepieces with less eye relief in the future if you prefer to bury your eye in the eyecup.

With the overall aging of the astronomy population, there is a lot of pressure on eyepiece companies to produce long eye relief eyepieces for eyeglasses wearers,

but there are still a lot of (still the majority) eyepieces with less eye relief.

As you get used to holding your head steady, this problem will go away.

 

In use, how to approach an eyepiece is this:

Start from too far back and approach until you begin to see the field of the eyepiece.

Get closer until you *just* see the edge of the field in your peripheral vision.  Stop there.

That is the "working" distance for that eyepiece.

 

If that seems too far out from the eyepiece, you can look into raising the eyecup with an eyecup extender, or get a longer eyecup from a dealer who sells such things.

Or replace the eyepiece with one having less eye relief.  Or get a long eye relief eyepiece that has an adjustable eyecup that can be raised sufficiently to make it comfortable to use.

There is always more than one way to get to the goal of comfortable observing.

 

  • Like 3
  • Thanks 2
Link to comment
Share on other sites

To add to what's been said - I find that otherwise comfortable eyepieces cause me similar issue with Mak102.

This is because of magnifying secondary mirror being so close (so I've been told) - which extends eye relief of eyepieces further - similar to what barlow does.

32mm Plossl is very comfortable eyepiece otherwise when used in different scopes - but in Mak it suffers from two issues - first is slight vignetting - Mak102 has slightly smaller fully illuminated field and can't use max field stop of 1.25" EP - this means 32mm plossl and 26mm ES62 will have this slight issue. Second is of course very long eye relief.

Upside is that eyepieces which have shorter eye relief in Mak feel more comfortable to use.

  • Like 1
  • Thanks 1
Link to comment
Share on other sites

Some very helpful replies, thank you.

Last night I adopted the advice given and enjoyed what was my best yet observing session, comfortably seated, telescope at the right height for viewing the Moon near to the zenith and the Mak mounted on an alt az rather than the usual EQ mount - this made a big difference in ease of use. I also adapted my viewing approach to suit the eyepiece rather than fighting it, this was better although still not ideal but, as has been said, I may get used to it over time.

Interesting point Vlav makes about the design of the Mak 102 possibly contributing to this effect, it will be interesting to compare the EP performance in my 80ED when I get it. 

For the inexperienced, it seems eyepiece selection is something of a lottery with potentially frustrating and expensive consequences. I wonder if there is a formula for determining an individual's EP eye relief requirements?

  • Like 1
Link to comment
Share on other sites

5 hours ago, Aquavit said:

For the inexperienced, it seems eyepiece selection is something of a lottery with potentially frustrating and expensive consequences.

The good news is that the market for good secondhand astro gear is strong. In fact, if you buy secondhand, you are likely to be able to sell if for the same amount.

 

  • Like 1
Link to comment
Share on other sites

8 hours ago, Aquavit said:

Some very helpful replies, thank you.

Last night I adopted the advice given and enjoyed what was my best yet observing session, comfortably seated, telescope at the right height for viewing the Moon near to the zenith and the Mak mounted on an alt az rather than the usual EQ mount - this made a big difference in ease of use. I also adapted my viewing approach to suit the eyepiece rather than fighting it, this was better although still not ideal but, as has been said, I may get used to it over time.

Interesting point Vlav makes about the design of the Mak 102 possibly contributing to this effect, it will be interesting to compare the EP performance in my 80ED when I get it. 

For the inexperienced, it seems eyepiece selection is something of a lottery with potentially frustrating and expensive consequences. I wonder if there is a formula for determining an individual's EP eye relief requirements?

No formula, but 10-15mm eye relief is comfortable without glasses, and 18-24mm with glasses.

Eye reliefs in excess of 24mm or shorter than 10mm are a problem.

  • Thanks 1
Link to comment
Share on other sites

4 minutes ago, Don Pensack said:

No formula, but 10-15mm eye relief is comfortable without glasses, and 18-24mm with glasses.

Eye reliefs in excess of 24mm or shorter than 10mm are a problem.

And take manufacturers claims of eye relief with a large dose of skepticism.  Most quote designed eye relief to the center of the eye lens, which can be much less than the usable eye relief if the eye lens is deeply recessed or deeply concave.

Link to comment
Share on other sites

10 minutes ago, Louis D said:

And take manufacturers claims of eye relief with a large dose of skepticism.  Most quote designed eye relief to the center of the eye lens, which can be much less than the usable eye relief if the eye lens is deeply recessed or deeply concave.

Wouldn't it be nice if eye reliefs were stated in terms of the optical configuration (from the glass) and the ergonomic configuration (from a horizontal line across the top of the eyepiece).

I would argue the 2nd eye relief should be measured from the folded down rubber eyecup, and not the aluminum below it.

  • Thanks 1
Link to comment
Share on other sites

1 minute ago, Don Pensack said:

Wouldn't it be nice if eye reliefs were stated in terms of the optical configuration (from the glass) and the ergonomic configuration (from a horizontal line across the top of the eyepiece).

I would argue the 2nd eye relief should be measured from the folded down rubber eyecup, and not the aluminum below it.

I'd also like standardization on how apparent field of view is measured and have vendors quote accurately measured numbers using this criterion for each and every eyepiece, not just for a particular eyepiece line as a whole.

That, and quote accurately measured effective field stops so users can calculate true field of view accurately.

Televue's specs are pretty close on these, so they could be held up as the gold standard for others to follow.

Link to comment
Share on other sites

4 minutes ago, Louis D said:

I'd also like standardization on how apparent field of view is measured and have vendors quote accurately measured numbers using this criterion for each and every eyepiece, not just for a particular eyepiece line as a whole.

Here is simple method of doing it (at least I think it is simple).

Requires way to measure distance and white circle on black background.

Test is conducted by standing in front of the wall with circle on it at some distance so that circle is approximately the size of quoted FOV. Now take eyepiece and place it in front of one of your eyes - as if you are observing thru it. You should see field stop of the eyepiece and out of focus light in FOV. Keep you other eye open and move forward/backward until two circles overlap.

Measure distance from your eye to circle on the wall and use diameter of circle to calculate angular diameter of circle at that distance.

This technique can be used to compare fields of view of two eyepieces. You don't need circle - just a blank white wall or any other background that will illuminate FOV properly. Place each eyepiece on respective eye like when binoviewing. You should be able to instantly tell which FOV is bigger since circles will overlap but have different sizes (or same size if FOVs are equal).

Link to comment
Share on other sites

Hi Aquavit, when I bought my 127 Mak, I also purchased a 32mm Skywatcher super plossl which I found to be very nice, but, like you I had difficulty with eye placement. I do not wear spectacles and the eye relief was just too much, resulting in black outs and kidney beaning.

Having read quite a few reviews, I bought a 30mm Vixen NPL plossl. This eyepiece has a twist up eyecup which extends quite a long way and I no longer have any problems at all with eye placement. 
The slightly smaller 30mm fov is hardly noticeable and the views really are bright, clear, and sharp, it even works well in my f4.9 102 Star Travel.

 I am still very much a beginner and find it hard to spot subtle differences in eyepieces, but I found this eyepiece so much to my liking that I have swapped most of my other eyepieces for Vixen SLV’s, which I really do like, and they also have similar twist up eyecups, which for me, provide very good eye placement.

  • Like 2
Link to comment
Share on other sites

On 24/02/2021 at 10:40, vlaiv said:

Here is simple method of doing it (at least I think it is simple).

Requires way to measure distance and white circle on black background.

Test is conducted by standing in front of the wall with circle on it at some distance so that circle is approximately the size of quoted FOV. Now take eyepiece and place it in front of one of your eyes - as if you are observing thru it. You should see field stop of the eyepiece and out of focus light in FOV. Keep you other eye open and move forward/backward until two circles overlap.

Measure distance from your eye to circle on the wall and use diameter of circle to calculate angular diameter of circle at that distance.

This technique can be used to compare fields of view of two eyepieces. You don't need circle - just a blank white wall or any other background that will illuminate FOV properly. Place each eyepiece on respective eye like when binoviewing. You should be able to instantly tell which FOV is bigger since circles will overlap but have different sizes (or same size if FOVs are equal).

I find this technique works well at 50-70°, but is difficult to gauge with 100-110° eyepieces.

  • Like 1
Link to comment
Share on other sites

On 24/02/2021 at 12:40, vlaiv said:

Here is simple method of doing it (at least I think it is simple).

Requires way to measure distance and white circle on black background.

Test is conducted by standing in front of the wall with circle on it at some distance so that circle is approximately the size of quoted FOV. Now take eyepiece and place it in front of one of your eyes - as if you are observing thru it. You should see field stop of the eyepiece and out of focus light in FOV. Keep you other eye open and move forward/backward until two circles overlap.

Measure distance from your eye to circle on the wall and use diameter of circle to calculate angular diameter of circle at that distance.

This technique can be used to compare fields of view of two eyepieces. You don't need circle - just a blank white wall or any other background that will illuminate FOV properly. Place each eyepiece on respective eye like when binoviewing. You should be able to instantly tell which FOV is bigger since circles will overlap but have different sizes (or same size if FOVs are equal).

I use the projection method followed by trigonometric calculations to get each eyepiece's AFOV to within a degree or so accuracy.

Once I have a baseline of reliable values for eyepieces within a given AFOV range, I can then use comparative analysis of my images of the AFOV to further refine the values within a group.  I divide the width in pixels of the most accurately known AFOV by two to get the opposite side value, accept the half angle from the projection method as accurate for the subtended angle, and then back-calculate the virtual distance to the image circle to get the adjacent side value.  I then use this virtual distance as constant across images and use the half-widths of the other AFOV images to calculate their half-angles for AFOV.  The AFOV calculations are accurate within the group.  Whether the AFOV values are absolutely accurate depends on the accuracy of the original eyepiece chosen as having a well known and measured AFOV.  That's how I got the values for my 26mm Meade MWA report.  Projection methods failed utterly with its massive SAEP.  There was no good way to measure the value via projection accurately for both full field with raging SAEP and easily seen field with minimal SAEP.  The main problem was the very indistinct exit pupil point that covers 12mm of distance according to Ernest in Russia.  This made measuring the adjacent value difficult.  Ernest made no attempt to measure the easily seen AFOV in his review that I could discern.

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share

  • Recently Browsing   0 members

    No registered users viewing this page.

×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue. By using this site, you agree to our Terms of Use.