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Moon through Kowa Prominar 883 + APM 12.5mm + 1.6x extender (1 Viewer)

Accipiter_22

New member
I had no chance to check how this combination performs at the night sky, and based on the current weather forecast for my area this wont change soonish. However, I used it quite a bit in the past days to read coded colour rings of gulls, and also on an overcast it works well (my locality is within the North Germain Plain ). The contrast is noticeably lower compared to a lower mag eyepiece and the same is obviously true for the brightness, given the small exisit pupil. Most importantly the image is still crispy enough that the high power is usable. Approximately one hour before sunset the limit is reached and there is no gain anymore in using this magnification. On a bright day it will be fine I guess, also for monitoring raptor nests. The main problem I would imagine then, is heat haze.
 

BoldenEagle

Well-known member
Couldn't you get any closer?

(you know I'm joking....)
Well, this is the best I can do at the moment:


I think this sample of 883 could handle even more than 96x when viewing bright objects like the moon, not so sure of terrestrial viewing because image will get so dim.

Juhani
 

Binastro

Well-known member
Juhani,

That is good performance shown on the video.
I watched it on the T.V.
Only slight turbulence.

The Seeing is quite good.

Does the focus change slightly as the eyepiece zooms?

It was minus 20C and windy yesterday in Helsinki, so that would affect the Seeing.

It is difficult to determine the actual magnification as that depends on the camera.

Regards,
B.
 

BoldenEagle

Well-known member
Indeed the seeing was good, in fact it may have been one of the best I have had (I don't observe moon that often). Temperature was about -5°C and just moderate wind. At first there was thin clouds passing by but after few minutes it was mostly clear, maybe some humidity in the air.

It has been mostly cloudy here in central Finland for a long time so when I was heading to a grocery store and saw that moon was visible, I came back and left my scope on the porch to cool down. I started maybe half an hour after. Lucky I did because after an hour or so, the sky was again all cloudy.

Yes the focus changes quite amount actually when zooming in, have to refocus every time. I don't remember it was so severe with other scopes I have used.

Regards,

Juhani
 

Binastro

Well-known member
Juhani,

The albedo of a full Moon is 0.12.
But the albedo of a half Moon is only 0.02.

The Earth is much higher.

So generally photos of the full Moon need approx. the same exposure for a photo as the Earth allowing for losses depending on Earth location.

But a half Moon is dimmer.

It seems brighter because we are using our night vision/eyes.

I wouldn't think that 96x terrestrially would look dark on a bright day, but it might when cloudy.

The only time I have seen perfect Seeing was a night in September in Finland.
But often it was very good.

Regards,
B.
 
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BoldenEagle

Well-known member
I wouldn't think that 96x terrestrially would look dark on a bright day, but it might when cloudy.
I was referring magnifications bigger than 96x. Allthough 96x already is too much on many normal birding times, mainly early mornings. On bright daytime 96x is very usable, allthough other factors may then have stronger negative effect, mainly heat haze etc. Still it will be quite dim, of course it depends what you are referring it to.

I can see smaller details on the moon up to 96x but in many birding situations I can see more details at lower mag. because there is not enough light available to benefit all the way to 96x.

Regards,

Juhani
 

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