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APM Ultraflat 30 mm: Initial impression

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#51 areyoukiddingme

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Posted 23 February 2018 - 02:27 PM

Seems like a great alternative to the 30mm XW, and may well be better.

 

Given the more than 70 degree apov, it would be a nice match with a set of Morpheus.


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#52 areyoukiddingme

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Posted 01 March 2018 - 01:14 PM

My UF showed up yesterday. Tried it out in the day time, and then under heavily moon-lit skies in my Televue 101 and 12.5" F5 reflector (with coma corrector).

 

Holding the eyepiece up to my eye along with my 30 XW showed that the field of view in the UF is indeed wider. If the XW is 70, then the UF appears to be about 72 degrees.

 

My first look was in daylight with my refractor looking at the local mountains. The UF put up a very nice view. Sharp images, very easy and comfortable to use, and sharp to the edge with a clear field stop. I see a small amount of pincushion distortion, but it's very tolerable and makes this an excellent day time eyepiece. Very little evidence of lateral color, and I could see no field curvature (but that's easily accommodated in the day time).

 

At night I compared the UF with 30 XW, 31 Nagler, and 27 Panoptic.

 

After the day time views, I was expecting a very strong showing for the UF. However, I found that the field stop was not crisp at night, giving the impression of a little vignetting. Again, the views were excellent. Little to no lateral color to be found, no field curvature that I could see (it may be there, but I can accommodate it if it is) and panning about the low distortion makes for a good experience that I find preferable to the Televues. The distortion looks very similar to the XW.

 

Despite being a slightly wider AFOV than the XW, under the stars I got the strong impression that the XW had the wider field. It was a little odd, and I think this might be attributable to eye relief. The XW seems to have more eye relief and to give a more immersive experience. 

 

I found that in use the UF gave a very similar feel to the 27 Panoptic. Both eyepieces are similar in size, and the field presents similarly. In fact, I'd imagine it would be quite easy to mistake one for the other.

 

Both of the Televues give more of a 'pop' to stars--color in red stars seems more apparent than both the UF and the XW. But the greater pincushion is also readily seen in panning.

 

Comparing the XW back and forth with the UF, the XW has very evident lateral color, astigmatism is the dominant aberration at the edge to my eye, and if I look for it, I know there's field curvature too. I compared some low magnitude stars around Sirius using the XW and UF several times trying to see if there was any difference in transparency. There were two stars in particular near Sirius that I could only get with averted vision with the bright moon. Comparing several times, I found those stars were very slight easier to pick up in the XW than the UF. This is something I will repeat later on a dark night.

 

My tentative early conclusion is that the UF compares directly with the XW for a lot less money, feels like a Panoptic in use, has a slightly fluffy field stop, and possibly slightly less transmission than the XW. But it lacks the very evident aberrations of the XW too.

 

After the day time test, I was just about ready to say goodbye to the XW, but after the night time test, and despite all the palpable negatives in the XW, I was surprised to find that I enjoyed the views in the XW more than the UF.

 

But it is early days and I will be doing a lot more comparing down the road. For the money the UF is a bargain--less new than a used Panoptic is a steal.


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#53 vkhastro1

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Posted 01 March 2018 - 06:43 PM

Excellent review !

I received my APM 30mm UF eyepiece.

Looking forward to doing my evaluation along with eyepiece comparisions (same eyepieces you have along with the ES 30mm 82°.

Need to wait for the upcoming new moon period (also hoping for warmer weather).


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#54 areyoukiddingme

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Posted 01 March 2018 - 10:56 PM

It will be interesting to compare notes . . . 

 

I put the flashlight on the eyepiece today. I can see some baffling in there. If it's possible to put in a slightly bigger baffle to decrease the vignetting I see, I'd consider doing it.



#55 Starman1

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Posted 03 March 2018 - 02:31 PM

A larger I.D. baffle may result in a lot of scattered light or edge of field aberrations.

Everything in an eyepiece is a compromise.

It sounds like the field stop is not in focus for Scott's vision.

Or, there is a QC variation from piece to piece.

It was in focus for my slightly farsighted vision.


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#56 areyoukiddingme

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Posted 03 March 2018 - 03:24 PM

My right eye is slightly far sighted, and my left is near . . . I'll try both when I get a chance to see if it might be attributable my vision putting the field stop out of focus.



#57 areyoukiddingme

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Posted 03 March 2018 - 06:31 PM

Couldn't help myself . . . I unscrewed the bottom element to check out the baffling. It turns out that there is a baffle machined into the housing that sits a few mm above the lenses. Installing a slightly smaller baffle would appear to be a possibility.

 

Also, given that the bottom screws out, I should be able to experiment with screwing it out a turn or so to see if the vignetting effect changes.


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#58 areyoukiddingme

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Posted 04 March 2018 - 11:27 AM

Well, screwing the barrel out did not appreciably change the vignetting I see.

 

However, viewing while there's no moon did improve things. Still a little bit of fuzz there, but it's quite tolerable.

 

I also tried both eyes and found that my near sighted left eye gave a sharper field stop. So, I think it's my vision that's affecting this, as Don suggested.

 

I'm very much warming to this eyepiece, and I'm finding it pairs well with the Morpheus (my 17.5 showed up yesterday and has a similar feel).


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#59 old_enough

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Posted 05 March 2018 - 03:31 AM

I would be interested to learn about a comparison of the APM eyepiece with the older Paragon 30mm. While designed by the acclaimed Thomas M. Back, the 30mm Paragon is seldom discussed. The 40mm seems to be more popular.

But the 30mm Paragon seemed to be maybe the best in its class before the UF 30mm arrived. So a direct comparison would be very interesting.

It is now hard to come by one (or two for binocular use) of the original ‘TMB Design’ versions, but exact copies are still available from TS in Germany.

Has anybody had the chance to compare these eyepieces yet? Or any thoughts on this?

Thank you,
Sebastian
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#60 lylver

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Posted 05 March 2018 - 05:51 AM

I know the design for both and I had a true TMB paragon (#294) that I had disassembled.

Paragon was created to fit TMB apos so f/7 minimum and minimal lens count.

As usual Thomas Back used all availables surfaces and relied on FMC or better AR treatment.

 

APM UF is dedicated to fast optics and low curvature scope (reflector or refractor). It is not optimal with refractor scope under 1m fl (in fact very similar behaviour)

I read about transmission : not highest but optimised for classic nebula rays (H-beta, O-III, H-alpha, S-II)



#61 old_enough

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Posted 05 March 2018 - 06:58 AM

Thank you Myriam!

 

I'll bite the bullet and buy a pair of the TS Paragon 30mm variant. They boast about the coatings which is consistent with your analysis. As ThomasM has a pair of APM UFs I hope we can do a comparison at one point.

 

Best,

Sebastian



#62 areyoukiddingme

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Posted 05 March 2018 - 11:41 AM

I know the design for both and I had a true TMB paragon (#294) that I had disassembled.

Paragon was created to fit TMB apos so f/7 minimum and minimal lens count.

As usual Thomas Back used all availables surfaces and relied on FMC or better AR treatment.

 

APM UF is dedicated to fast optics and low curvature scope (reflector or refractor). It is not optimal with refractor scope under 1m fl (in fact very similar behaviour)

I read about transmission : not highest but optimised for classic nebula rays (H-beta, O-III, H-alpha, S-II)

 

Where are you getting the information about it not being optimal in scopes with less than 1m of focal length?

 

I'm finding it performs very nicely in my 540mm and 480mm refractors.



#63 lylver

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Posted 05 March 2018 - 01:29 PM

On the APM site :

 

APM Ultra Flat Field 30mm Eyepiece 70° FOV

High-quality eyepiece with long focal length!

The 2" 30mm UltraFlat Field Eyepiece features a high quality standard and a very compact design, which is designed to remove the field curvature at the edge, resulting in a flat, distortion-free image up to the edge of the visible field of view, even in very fast (for example  f/4) telescopes. The eyepiece has over - sized eyepiece lenses for the largest possible field of view and a 22mm eyerelief - also suitable for spectacle wearers, the foldable eye-rubber allow a comfortable view. All lenses (9 lenses in 5 groups) have a braod-band-multicoating (FMC) and blackened lens edges. The plug-in sleeve is equipped with a thread for 2 "filters.
The eyepiece is ideal for optics with medium or long focal length.

and see Mark comments

https://www.cloudyni...ions/?p=7826734


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#64 areyoukiddingme

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Posted 05 March 2018 - 02:08 PM

Interesting. I'm thinking that the slight vignetting of the field stop I'm seeing might be attributable to my secondary in my reflector being a little undersized. The field stop does seem more crisp in my refractors.



#65 lylver

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Posted 05 March 2018 - 02:34 PM

Maybe : you can check illuminated field on a newton with this link : 30 arc minute (moon) is the most frequent for visual for the 100% illuminated field. It is acceptable down to 75-70% for the outside part to the field stop

https://stellafane.o...b/newt-web.html

 

On my temporary newton 150/750 : size of the secondary 50mm for photo, 43mm for visual (165mm from secondary to focus)

 

Too small secondary : cause vignetting @ 5mm exit pupil.
Suitable size (my case) is 43mm secondary. It gives vignetting AFOV of 65°/28mm field @f5 for me, a good compromise

 

Too big secondary : shadow of the secondary visible. It is annoying with long fl EP.



#66 areyoukiddingme

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Posted 31 March 2018 - 03:31 AM

An update . . . I took the APM 30mm with me to Australia where I used it in an 8" F6 Dobsonian.

 

The eyepiece performed very well in that scope. Perhaps a touch of hairiness to the field stop still present, but this could just be my eyesight. In any case it didn't bother me at all. So I'm starting to think the "medium to longer focal length" statement rings true.

 

The APM put up wonderful views of eta carinae, omega centauri, a load of objects in the small Magellanic cloud and other southern sky show pieces. I particularly enjoyed using it with the cup folded down. The eyepiece showed good sharp views to the field stop, with just small amounts of coma seen at F6.

 

Since returning to California, I've also been using the APM in my 80mm F6 refractor, and I'm finding that the eyepiece does put up a surprisingly flat field. This scope has a lot of field curvature at 480mm of focal length, but this eyepiece seems to deal with it particularly well.

 

Tonight I measured the apparent field using the flash light technique and got 75.33 degrees, a nice chunk better than the advertised 70.

 

[the technique involves pointing the eyepiece at a wall with a flashlight shining into the bottom. You then measure the distance from the exit pupil to the wall, and the radius of the projected circle. The AFoV = 2 x arctan(r/d) where r = radius of the circle, and d = distance from the exit pupil to the wall).

 

There's a fair amount of error in the measurement, but probably right to +/- 1 degree, and certainly better than the advertised 70 degrees. As such it complements the Morpheus line very nicely (also took the 17.5 Morpheus). Having tried the 14 and 17.5 Morpheus, paired with the APM the Morpheus are a nice alternative to XWs.

 

Perhaps APM will do a 40mm in the future. . . 


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#67 Piero DP

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Posted 25 June 2018 - 05:44 PM

Any new reports for this eyepiece?
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#68 Kunama

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Posted 26 June 2018 - 06:10 AM

I just received a pair of these eyepieces yesterday, tried them out in the binoculars (at 30x) but due to the near full moon I really cannot give a review other than to say that they are very sharp on axis, seem well made and have good eye relief.  I think they are actually wider than the 70 degree inscription on the eyepiece states. My guess would be around 74 degrees.

 

Looking forward to getting them under a dark sky....


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#69 vkhastro1

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Posted 26 June 2018 - 06:18 AM

Looking forward to your review.

 

Happy birthday Matt smile.gif


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#70 rogeriomagellan

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Posted 28 June 2018 - 07:57 AM

Looking forward to your review.

 

Happy birthday Matt smile.gif

Hi.

 

Haven't you been able to make a comparison with the ES 82° 30mm yet?



#71 oldtimer

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Posted 02 December 2018 - 12:17 PM

I have a 100mm f4.5 RFT scope. (not the ES). MY Olivon 8 element 22mm 70 degree performs extremely well with little edge distortion. But now I've gotten greedy for more FOV. I just popped for the APM 30mm flat field. This will be a really tough test for this eyepiece so I'll keep all posted.  OH and I like the idea of a slight yellow cast which may assist the #8 yellow filter I'm now using to curb CA 


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#72 Starman1

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Posted 02 December 2018 - 01:31 PM

APM is now saying:

 

38mm field stop

75° AFoV

9 elements in 5 groups

eye lens 32mm

eye relief 22mm

 

The eye relief claim of 22mm is consistent with a 72° AFoV on a 32mm lens, but not 75°.

75° is consistent with a 20.8mm eye relief.

So, is the eye lens measurement wrong, the AFoV, or the eye relief?

Whatever it is, it's >70°.


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#73 Tamiji Homma

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Posted 03 December 2018 - 10:53 AM

I did APM 30 UFF AFOV measure by flash light method some time ago.

 

large.jpg

 

Tammy


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#74 range88

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Posted 03 December 2018 - 11:07 AM

APM is now saying:

 

38mm field stop

75° AFoV

9 elements in 5 groups

eye lens 32mm

eye relief 22mm

 

The eye relief claim of 22mm is consistent with a 72° AFoV on a 32mm lens, but not 75°.

75° is consistent with a 20.8mm eye relief.

So, is the eye lens measurement wrong, the AFoV, or the eye relief?

Whatever it is, it's >70°.

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#75 Starman1

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Posted 03 December 2018 - 11:14 AM

Someone else just measured his and got 73°, so we have 70.2°, 71.2°, 73°, 75.33°, and a guess of around 74°

Egads!

The engineering diagram also shows a 30.4mm field stop, but APM now claims 38mm and someone else calculated 36.4mm.

Was there ever a more confusing eyepiece?

At least we know the eye lens is 32mm wide.  And it has a long eye relief.

The rest?


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