I live in a suburban environment close to a natural reserve that hosts a good diversity of flora and fauna. I have been into backyard Astronomy for many years but it is only until recently that I started doing terrestrial observing. For that purpose a few months ago I purchased a Pentax PF-80ED-A spotting scope and I have been very pleased with its performance. However, because of my daily routine I generally observe at dusk and at night when the small aperture of the 80mm scope becomes a severe limitation. Fortunately I was able to adapt my smaller SCTs (6” and 8”) for doing terrestrial observing in low-light conditions with excellent results. Alas, most of the year it is humid here and I can’t use my SCTs for terrestrial observing in bad weather! For that reason a few days ago I purchased brand new a Celestron #52306 Regal M2 100ED spotting scope hoping that the additional 20mm of aperture (over my Pentax 80ED spotting scope) would allow me to continue to observe in rainy, low-light conditions as long as I can keep realistic expectations of what can be seen with this small aperture in those circumstances.
Here is a link to the product that I purchased:
After using the new scope (Celestron Regal M2 100ED) for the first time while looking at various stationary terrestrial objects at night (in good weather), it became quite apparent to me that the scope is probably not using the full aperture to produce the images. To confirm my perception, the next time I setup the Celestron Regal M2 100ED scope next to my Pentax PF-80ED and did a side-by-side comparison (at night, in good weather with the same stationary objects that have different levels of illumination) using their respective zoom eyepieces at the same magnifications and in most cases the images in both scopes were more alike than different, showing similar image brightness and resolution, with a slightly brighter image provided by the Celestron, but not what I would expect from a 20mm aperture gain –I can easily see the increase in image brightness when I compare my TV-85 next to my ED100SF and that’s only a 15mm difference!
So, if you are considering the Celestron Regal M2 100ED spotting scope for observing in low-light conditions, my first caveat would be that the scope may probably not be taking advantage of the full 100mm of aperture to produce the images.
See another user’s comments on the subject here:
Although the Celestron Regal M2 spotting scope line is supplied with a decent quality zoom eyepiece, one of its pros over other spotting scopes of similar cost is the ability to use 1.25” eyepieces designed for astronomical telescopes. As an owner of two Pentax spotting scopes that have this feature I was looking forward to use my astro-eyepieces with the new scope to try to extract the best possible images. Alas, the implementation of the eyepiece holding collar is quite different in both brands. While with the Pentax scopes you only need to drop an eyepiece into the eyepiece holder and then gently turn a knurled ring to lock it, the Celestron Regal requires you to press with some force on the eyepiece to fully seat it into the holder (else it springs back up because of an o-ring placed inside the holder) while at the same time you need to do quite a few turns of the locking collar to secure the eyepiece –if you do not seat the eyepiece properly, it won’t come to focus. On my Celestron Regal 100ED I need to press on the capped eyepiece top with my chin while I hold the scope body with one hand and turn the locking collar with the other. After all the trouble doing a few eyepiece exchanges I decided to abandon my initial plan of using my favorite astro-eyepieces with the Celestron Regal M2 100ED and simply use the included zoom eyepiece.
So, if you are considering the Celestron Regal M2 100ED spotting scope for its ability to use 1.25” eyepieces for astronomical telescopes, my second caveat would be that the way that the eyepiece holder of this scope is designed makes it difficult for frequent eyepiece swapping.
Other options and conclusions:
Before I purchased my Celestron Regal M2 100ED I was aware of these caveats from two owner’s comments but somehow I was hoping that Celestron would have dealt with the issues by now. Now I realize that I was probably too optimistic! If money was no object, I would have purchased a Pentax PF-100ED spotting scope that most owners/users agree it is a very good scope and be done with it, but unfortunately it is beyond my reach for using it just as a recreational terrestrial scope and also it does not come in an angled version. Even after these caveats, I see no other waterproof spotting scope options with ED glass for use in low-light conditions within my budget that would have been an improvement in light gathering capacity over the Celestron Regal M2 100ED, so I will probably stick with the scope and hope for the best!
I do not want to start a discussion about the merits of one type of telescope over the other (e.g. astronomical vs. spotting, catadioptric vs. refracting, etc.). I just want to let prospective buyers know about the limitations of the scope model that I purchased so they can make a more informed buying decision, that’s all.
Here is a picture of my newly acquired Celestron Regal M2 100ED spotting scope.