11 replies to this topic

[new2scopes]

Hello all. I am in the hobby just under a year and it is my first time posting here. Please forgive me if I have posted this in the wrong area of the forum, or if this has been asked and answered 

 

For background, the hardware I am using is a Takahashi FC100DF, with a Tele Vue Everbrite 2" diagonal. I have happily used the setup with a 16.5 MM Pentax SMC XW, but had only ever aimed the setup at the night sky. Recently, I acquired the same eyepiece in 23MM. and as I was aligning the scope with a new finder, during the day, I noticed what I would assume is vignetting. I would best describe it as a reddish-brown ring around the edge of the image. I thought maybe it was an issue with the eyepiece at this focal length or an issue with the eyepiece itself, so I tried my 16.5 and saw the same thing. I've been perfectly pleased with the 16.5 during normal night use. I have not gotten a chance to try the 23 MM for night viewing yet, because it has been overcast for days here in NJ.

 

My question is, is this normal behavior for a wide field eyepiece during the day? I did not see this ring during the day, with my Panoptic 27 MM.

[areyoukiddingme]

I've not noticed this through the day, but it sounds like the "ring of fire" effect--chromatic aberrations at the edge of the field. The 31 Nagler shows it strongly during day-time usage. 

 

The 23mm XW does have a vignetting effect. I found it rather obvious, but others don't notice it, so I suspect there's something going on with differences in eyesight.

 

Welcome to CNs!

[SeattleScott]

Yes this is common for many premium ultrawide eyepieces when used during the day, or on the Moon. Especially longer focal lengths.

If one wants to do terrestrial viewing, they usually want narrower AFOV.

[new2scopes]

Thank you for your insight, gentlemen. It sounds like it's a safe bet that if I did not see this reddish-brown ring at night in the 16.5 MM, I won't see it at night in the 23 MM.  Would you agree? If that's the case, then I'm good, since my purpose is viewing the night sky. 

[areyoukiddingme]

Yes, night time will be fine. You might see some of the vignetting effect, however.

[Starman1]

Hello all. I am in the hobby just under a year and it is my first time posting here. Please forgive me if I have posted this in the wrong area of the forum, or if this has been asked and answered

For background, the hardware I am using is a Takahashi FC100DF, with a Tele Vue Everbrite 2" diagonal. I have happily used the setup with a 16.5 MM Pentax SMC XW, but had only ever aimed the setup at the night sky. Recently, I acquired the same eyepiece in 23MM. and as I was aligning the scope with a new finder, during the day, I noticed what I would assume is vignetting. I would best describe it as a reddish-brown ring around the edge of the image. I thought maybe it was an issue with the eyepiece at this focal length or an issue with the eyepiece itself, so I tried my 16.5 and saw the same thing. I've been perfectly pleased with the 16.5 during normal night use. I have not gotten a chance to try the 23 MM for night viewing yet, because it has been overcast for days here in NJ.

My question is, is this normal behavior for a wide field eyepiece during the day? I did not see this ring during the day, with my Panoptic 27 MM.

It is not desirable to have vignetting, but it is not uncommon.
I noted it in the 23mm in my review of the 85s a couple years ago. It can be seen at night, though you really have to look for it. It just means the eyepiece is not a good choice for daylight observations.
For what it's worth, there are a lot of nice astronomy eyepieces that don't work well for daytime use.
I didn't see it in the 16.5mm at night at all, so if it vignettes, it must be a significantly lesser amount than in the 23mm.

[new2scopes]

Thank you very much for your reply, it was very helpful to me. I am keeping the 16.5, I have really enjoyed the views through it. The 23 mm is still within its return period, so I shipped it back this morning to exchange for a 22 MM Nagler.

[mikeDnight]

Vignetting appears as a dimming of the edge of field. The fact you describe it as red/brown has me wondering if it isn't lateral colour you're seeing,  which all wide angle eyepieces show, including the 22 Nag. You may have returned a perfectly good eyepiece. Your TV diagonal shouldn't Vignette, so what's causing vignetting?

Edited by mikeDnight, Yesterday, 10:01 AM.

[new2scopes]

I'm sure it was working as intended and would likely not impacted my night time viewing. However, I do see a considerable amount less of that ring in the Nagler 22MM I purchased.

[Starman1]

Vignetting appears as a dimming of the edge of field. The fact you describe it as red/brown has me wondering if it isn't lateral colour you're seeing,  which all wide angle eyepieces show, including the 22 Nag. You may have returned a perfectly good eyepiece. Your TV diagonal shouldn't Vignette, so what's causing vignetting?

I saw noticeable vignetting in the 23mm as well.  I think its intrinsic to the eyepiece and likely indicates the focal length and or apparent field was pushed a little bit too far.

I did not use it in daylight to see if there was chromatic aberration of the Exit Pupil (CAEP), but CAEP is present in many ultrawide eyepieces, including the 31mm and 26mm Naglers, the 30mm ES UWA, and the 28mm 82° from various labels.

That provides a tint to the outer 10° of field or so, and can be seen in daylight use.

[SeattleScott]

I'm sure it was working as intended and would likely not impacted my night time viewing. However, I do see a considerable amount less of that ring in the Nagler 22MM I purchased.

The T4’s are a different optical design and seem to have less ring of fire than T5s, ES 82, etc. Great eyepieces, but not for terrestrial viewing.

But yeah you wouldn’t see it at night except for on the Moon.

[DRodrigues]

The T4’s are a different optical design and seem to have less ring of fire than T5s, ES 82, etc. Great eyepieces, but not for terrestrial viewing.

...

The N22 is good for day-light use. The N17 wasn't due to black-outs...