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Old Sep 15, 2003, 11:50 AM   #1
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Default ETX 90RA/CP 4500 focusing questions

We are looking into an ETX 90RA telescope and Nikon Coolpix 4500 camera coupled with the Williams Optics/Scopetronics eyepiece for terrestrial digiscoping. We are hobbyists and have gotten quite a bit of useful information from your forum. We do have some questions.

Is focusing a series issue with this setup (forgetting extraneous factors, such as atmospheric conditions)? We have had limited experience with the Sony F707 and the ETX 90RA and have found that a good sharp picture was generally the exception rather than the rule even though everything seemed to be in focus.

What is the practical range of distances within which this combination is most effective? We have found that at distances of up to 50 feet, we can get “count-the-feathers” sharpness with the Sony and a B-300 teleconverter. What we would like to get are sharp pictures of eagles, hawks, and other birds and wildlife that spook easily and won’t sit still within this distance.

In some posts, we have read distance references such as “6000 mm equivalent”. What does this mean?

Thanks for your help.

Dave (grizzlyike)
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Old Sep 18, 2003, 8:12 AM   #2
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Hi Dave,

It's definitely possible to get 6000mm "equivalency" with this combination. What that means is simply that we are dealing with two issues: first we have the true focal length of the telescope with eyepiece attached, then we have the CP4500 which has a "true focal length" starting around 7.8 mm at wide angle which "corresponds" in terms of field of view to an SLR at 38mm. At the 4x+ telephoto end we have about 32 mm true focal length which corresponds to around 155mm field of view in 35mm terms.

This is probably not the place to go into the details of "equivalency" but suffice it to say that through a combination of electronic magnification and optical magnification you actually do get identical magnification as if you were shooting a 35mm film camera at 6000mm true focal length with this combination.

How far you can actually be from the subject and get satisfactory results is identical to what you would be able to do under same conditions with a telescope which had a focal length of 6000mm. Atmospheric conditions really play into the results in a big way. Thermal polution, haze, camera shake, etc., is all greatly magnified which using high powered optics terrestrially. This is even more so than when shooting celestial objects.

By using the Xtend-a-View to get a 2x magnification of the LCD image, focusing is not terribly difficult. It does take practice and at these focal lengths even slight motion is greatly magnified so that a rock-solid tripod and remote release are strongly suggested. The more you do this, the better you get at it and practice does indeed greatly increase your chances for success. Yes, even after doing this for a number of years I still miss a shot once in a while, but I get far more "keepers" than misses. Not so different, really, than general photography.

Typically, the best results are obtained at relatively close distances such as up to 100 yards or so. Following are three images in this order:

1. 2000 mm focal length with my D30 and Meade ETX-90
2. 2300 mm focal length with my CP990 and Meade ETX-90
3. 5989 mm focal length with my CP990 and Meade ETX-90

The second and third image using William Optics DCL-28 - DigiSnap 2000 release and Xtend-a-View for LCD focusing.


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Old Sep 19, 2003, 5:58 PM   #3
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Default ETX90 & Coolpix 4500 Additional Questions


Thank you for your timely response. I appreciate the effort and obvious thought you put into your reply. Now that I have the ETX90 and the Coolpix 4500 in hand, do you have any thoughts on the threaded eyepieces offered by Williams Optics and Scopetronics. Is there a significant difference between the 14 mm and 18 mm? I plan to get one or the other.

I would also like to know if you have any opinions on the MaxView 40 with this scope and 4500 camera. I originally purchased that eyepiece to use with my Sony 707 and wonder if it has any application with the Coolpix. I would, of course, need to purchase a new step ring.

I enjoyed your comments regarding focusing. Any tips you can provide to steepen the learning curve will be appreciated. So far, my "misses" far exceed my "keepers". In fact, this experience prompted me to purchase the Coopix 4500. The other day, I scoped an Osprey at 100+ yards with the ETX 90 and a 26 mm plossl eyepiece. The image was crystal clear and bright (I literally could count the feathers). I asked myself - how do I get my digital camera to capture this exact image? I plan to keep trying.

Again, thanks for your help.

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Old Sep 19, 2003, 8:35 PM   #4
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My suggestion would be to get the William Optics DCL-28 which is a 24mm eyepiece. The ScopeTronix 14mm and 16mm (I have all three of these) has too much magnification for the 4x zoom. The DCL-28 gives 5898mm with the 3X CP950/990 and you really can't even use the full zoom of the CP4500 with it.

The Max40 "can" work, but doesn't provide enough focal length for the CP4500 - it's really much better with the 5x Sony, etc., but you could simply hold the camera up to it and give it a try to get a feel for what the results would be.

Best regards,

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Old Oct 9, 2003, 5:31 PM   #5
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A question, is possible the use of this telescope with a eyepiece of 2" (William Optics DCL-52) . I have one that has a great field of vision and camara FZ1 without viñeteo would allow me to use it my along with or that I think...

If this eyepiece can be connected, that is what necessary. Thanks in advance, I am inexperienced and my English is very bad; -)
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