General spotting scope questions (1 Viewer)

[kimsrk]

Hi Steve,

First off, does your scope come into sharp focus at 75x when viewing at closer distances, where air quality is less of a factor? Or do you need to hunt and not really achieve a distinct point of best focus? Second, have you looked inside the scope for any obvious issues?

No obvious issues, but yes sometimes it seems like I do need to hunt a little at max zoom. Especially compared to lower zoom viewing where the image will pop nicely into focus.

2) One mile is quite far for objects that small, especially if there is mirage or heat haze! And if there is sea spray, fog, particulate, etc. it can be difficult as you are literally looking through all that "stuff".

Yeah I've just accepted this is the case, it's just a little frustrating because it's allllmmmooosst there. Like if I could squeeze out a tiny bit more detail, I could definitely ID at least a few of them. I was able to read a medium sized sign on the island, relatively easily which was pretty cool. I couldn't even see the sign with the naked eye.

3) I have owned seven Nikon Fieldscopes and don't recall any of them with that drastic of drop in contrast. I sometimes take a new-to-me scope to a local duck pond, after doing a star test and resolution comparison against a known scope. The image I get from my ED82-A when viewing some of the waterfowl in the sun is sometimes hard to believe as it is incredibly vibrant. However, there are times where some scenes and objects are dull even with the 82mm. The quality of the light, clean/dirty air, and I'd imagine the human eye and brain all factor into it.

My ED82, is absolutely stunning at some distances and viewing conditions. Perhaps I'm just asking too much from any scope, honestly, because within 100ish yards I love the view. I really just want to compare it to a newer one to really know if I'm just asking too much. I am a newbie.

If you are super curious, you can read about "star testing". Just do a search here. There are some good threads, sample pictures, and reasons why it is relevant in finding lemons quickly without having to spend days, weeks, or months wondering if you have a bad sample. But first, I would just check to see if you can just get sharp focus at 75x before doing anything more elaborate. You could even use a dollar bill as a target across a large room. You should be able see all sorts of defects in the print, with more and more detail at progressively higher magnification. It definitely helps to have a really good scope for comparison though.

The star test I did with a flashlight didn't show anything obviously wrong. Pretty cool test.

And if you want to compare, there are companies that allow you to rent a scope! But you might get an alpha lemon!

Jason

Yeah, I'm keeping this one for now, the price was definitely right.

Thanks so much for sharing your information.

Steve

 

[4th_point]

Perhaps I'm just asking too much from any scope, honestly, because within 100ish yards I love the view. I really just want to compare it to a newer one to really know if I'm just asking too much. I am a newbie.

Steve,

I understand what you are conveying, but you actually want a well corrected scope to compare to. A new spotting scope doesn't guarantee much, unless it has been verified or validated.

As Hermann pointed out, you actually have an alpha class scope currently in your possession. But something doesn't add up with your scope. You should not have to hunt for best focus on 75x. Unless the focuser is sticky. What you describe sounds just like a scope that has some aberrations that are affecting performance. How many rings did you view for your test?

Jason

 

[kimsrk]

Steve,

I understand what you are conveying, but you actually want a well corrected scope to compare to. A new spotting scope doesn't guarantee much, unless it has been verified or validated.

As Hermann pointed out, you actually have an alpha class scope currently in your possession. But something doesn't add up with your scope. You should not have to hunt for best focus on 75x. Unless the focuser is sticky. What you describe sounds just like a scope that has some aberrations that are affecting performance. How many rings did you view for your test?

Jason

You know, you asking that made me reevaluate what I saw, I'm going to have to revisit the test at some point in the future. When I took another look I actually had a very hard time distinguishing the first 3-5 rings that appear. I found I could never quite get them in focus to see them individually. It seems like there is a lot of technique involved to evaluate this properly and I don't have it yet.

Steve

 

[kimsrk]

Steve,

I understand what you are conveying, but you actually want a well corrected scope to compare to. A new spotting scope doesn't guarantee much, unless it has been verified or validated.

As Hermann pointed out, you actually have an alpha class scope currently in your possession. But something doesn't add up with your scope. You should not have to hunt for best focus on 75x. Unless the focuser is sticky. What you describe sounds just like a scope that has some aberrations that are affecting performance. How many rings did you view for your test?

Jason

It's been a while but I finally got the start test figured out and had another ED III sample to test against.

The original 82 ED III I bought definitely shows its flaws in the test. There is some pretty obvious coma and spherical aberration with this unit. It was even more obvious next to a better specimen. In contrast, on a 60 ED III I picked up, there is clearly no coma. Nice even, bright, perfect-ish circles, with probably a touch of under correction and moderate spherical aberration. And as you might expect, at max zoom it snaps nicely into focus with much better clarity and resolution, no hunting. It actually resolved small distant lettering at 60x better than the 82 did at 75x.

Now the question is what to do with the poor copy, if there is anything to be done. I'm considering seeing if getting it collimated by suddarth would be worth my time.

Thanks for letting me know about the star test, it is now something I will always be using for any future scope optics.


Steve

 

[Binastro]

If the out of focus stars are central with no signs of offset then it is in collimation.

The only possible tweak would be changing the separation of the elements, but repairers may not routinely do this.

If the scope is a poor sample it is likely the objectives or other elements are just poor quality, and nothing can be done without refiguring and it may be the glass has striations.

It might work at low magnifications quite well.

If the scope is actually out of collimation then collimating will help, but the scope may still not be the best.

Regards,
B.

 

[kimsrk]

If the out of focus stars are central with no signs of offset then it is in collimation.

Could you explain this a little more? Specifically what would offset look like?

I've never found consistent information on if coma can be corrected by collimation.

Lockwood Custom Optics - Why aren't my stars round?

This source indicates that they can be related. But I have also read otherwise. So do I just have an unfixable dud?

Steve

 

[Binastro]

If the central point is central for a central star in the expanded disc with no offset then the scope is collimated.

If the scope is out of collimation then there will be more one sided errors.

If the scope is collimated there can still be coma, which should look the same all around.

I do not know the intricacies of all optical aberrations.

Perhaps buy Suiter's book.

I think 'Star testing astronomical telescopes'.

Regarding unobstructed telescopes.

I wouldn't say that you may have a dud, as many spotting scopes seem to be less than optimal.
Good observations can be made with rather poor telescopes.

Also adjusting and testing astronomical objectives H.D, Taylor around 1890? but available in modern editions.

Regards,
B.