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testing apo optics in daylight?

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#1 NHRob

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Posted 05 August 2014 - 02:52 PM

Well, I am going nuts ...   It's been over a month since I've gotten my FS-102 and I have yet to be able to test the optics

at night.  The weather pattern has been awful (many clear days, cloudy nights).  The few nights it was nice, I couldn't take the scopes out fo rother reasons.

I am waiting to be able to critically compare the optics in my SV-105T against the FS-102.

 

What would be reasonable daytime targets for doing so?

I am in a rural area with lots of trees.  Have been thinking of just viewing small tree limbs and leaves that are very distant ... looking at sharpness/contrast.

 

 

 

 



#2 Jon Isaacs

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Posted 05 August 2014 - 04:39 PM

Rob:

 

You can do a star test by looking at the specular reflection off a distant power line insulator. You can test the color correct by observing a power line against the blue sky...  You can enjoy the views by looking at birds...

 

Jon



#3 Bob D

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Posted 05 August 2014 - 09:33 PM

I used to test my telephoto camera lenses by photographing pages of newspaper want ads (large area of uniform font) tacked to the fence across the backyard.  Of course, you could just do this visually, but it was easier to do the comparisons of various lenses in the center and corners of the FOV with the photos.  I did this with lenses up to 100mm aperture and up to 2000mm focal length (including teleconverters).  Some of them were kindly taken back my friendly camera store owner after I showed him poor results.  He sometimes let me take three of one kind to test, hoping that I would buy the best sample.  I appreciated that arrangement!



#4 WebFoot

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Posted 05 August 2014 - 11:14 PM

Keep in mind that convection currents are more common during the day, messing up the "seeing" if you're in a sunny place.



#5 SteveC

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Posted 05 August 2014 - 11:54 PM

Rob:

 

You can do a star test by looking at the specular reflection off a distant power line insulator. You can test the color correct by observing a power line against the blue sky...  You can enjoy the views by looking at birds...

 

Jon

I checked out my TEC110 by looking at turtle heads, they have weird eyes. 



#6 NHRob

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Posted 06 August 2014 - 06:19 AM

Nice suggestions.  Thanks guys.  I don't have a power line insulator anywhere nearby but I can try power lines.



#7 Illinois

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Posted 06 August 2014 - 06:44 AM

I did test on far away trees and see leaves as clear and sharp. I also homemade black dot  about 1/4 inch diameter on about 10 inch square white cardboard and 3 feet post. Put it as far as you can (200 feet away if you can) and you can test to see black dot. I did two black dots and its about 2 inch apart so I can see double star!


Edited by Illinois, 06 August 2014 - 06:45 AM.


#8 tomcody

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Posted 06 August 2014 - 09:04 AM

Rob,

I use my Taks during the daytime  a lot, some good targets are moss and bark on branches, ants and other insects in trees, ( birds are hard to target unless you have a good alt-az) and leaf  vein structures 

One to two hundred feet is a good distance for these targets ( I like to read the vin number plate on my neighbor's truck at about 150 ft once in a while), although four to five hundred feet is doable but with some loss of comparative detail, I found that bark and moss give good indications of your optics as they usually have some hard edges with sunlight/shadow shading visible.

About 50-100x is a good daylight range. Have fun with it, I keep a couple of scopes set up in the house and for quick looks, just remove a window screen and open the window.

Rex

PS This reminds me of a day when I was using my 12" Meade LX200 from inside the house,to read insulators and the printing on phone company cables on poles about 600 ft away, I started to observe a black bird sitting on a phone cable and at that distance my FOV was restricted to half the bird (either feet or head) when I looked at his feet, the bird was at ease and stayed put but,when I looked at his head he turned his head so one eye faced me, got a worried look and moved down the wire until he was out of the scope's FOV, this happened  four or five times and convinced me he could see me looking at him, maybe he saw a 12" eyeball ? and freaked out?

Rex

PPS here is a pic with my FS128/Leica zoom shot with a IPhone at 140ft (its not perfect its harder than it looks to hold the phone at the right place without a bracket).

I was trying to photograph an ant on that branch ( the branch is about twice as wide as  the length on an ant), never got him to stay in view while I snapped a pic.

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Edited by tomcody, 06 August 2014 - 11:53 AM.


#9 t.r.

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Posted 06 August 2014 - 09:53 AM

Keep the Faith Rob, our "good observing" weather of Fall is coming!  



#10 Scott99

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Posted 06 August 2014 - 10:49 AM

Keep the Faith Rob, our "good observing" weather of Fall is coming!  

I'm wondering if the fires in the West are degrading our transparency.  Will probably continue into late fall/early winter unfortunately.

 

the humidity the last few weeks has been bad though, shouldn't last too much longer.



#11 SteveC

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Posted 06 August 2014 - 12:00 PM

Rob,

 

This is the artificial star I own, if you need to borrow it.

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#12 NHRob

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Posted 06 August 2014 - 01:09 PM

Another thing I could use for testing contrast and scatter, is to make a black box.  Use a white cardboard surface and make a small circular aperture in it, maybe 0.1" diameter.

Behind this hole, place a black box.  This is easily made with spare flocking material.   View this at 50 - 100 ft and evaluate contrast between the black hole and white surroundings.



#13 skysurfer

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Posted 06 August 2014 - 01:46 PM

Daylight start test ? Use real stars.

Mag 0 or 1 stars are easy to find in daylight as long as you know where to search, particularly with low (< 30 degrees) Sun. In a 10cm Arcturus or Vega appear very bright with 40-80x magnification, including the Airy disk on an early evening / late afternoon this time of the year !

 

Look how: http://skysurfer.eu/daystars.php


Edited by skysurfer, 06 August 2014 - 01:47 PM.


#14 gnowellsct

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Posted 07 August 2014 - 12:56 AM

Well, I am going nuts ...   It's been over a month since I've gotten my FS-102 and I have yet to be able to test the optics

at night.  The weather pattern has been awful (many clear days, cloudy nights).  The few nights it was nice, I couldn't take the scopes out fo rother reasons.

I am waiting to be able to critically compare the optics in my SV-105T against the FS-102.

 

What would be reasonable daytime targets for doing so?

I am in a rural area with lots of trees.  Have been thinking of just viewing small tree limbs and leaves that are very distant ... looking at sharpness/contrast.

 

 

Along the same lines as a power line: Roland Christen recommends an isolated tree branch against a blue sky.  This is a very difficult optical test not just for scopes but for binoculars--maybe cameras too!

 

One word of warning.  If you look at a *tree* against a blue sky you may be aghast at the result.  The reason is that the tree is in effect a bubble of branches (I'm thinking a leafless tree here in fall or winter or early spring) and the closest branches may be 50 to 100 feet closer to you than the furthest branches.  When you are looking through the bubble of branches you are almost sure to get color aberration because you have a variety of focal points spread across a wide area, and no decent (lens) scope can bring all those color lines to focus for the entire diameter of the tree.  As you fiddle with focus in this kind of situation, you may find all in the same view foreground color aberration, background aberration, and zero aberration at the point of focus.  

 

Kinda cool.

 

Greg N



#15 mogur

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Posted 07 August 2014 - 07:27 PM

Why is everyone suggesting a black object on a white background? It would seem to me that if you wanted to simulate actual star gazing you would use a white object on a black background. :shrug:








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