Telescope Reviews: More on the Garrett GT-100

I took a few moments tonight to test the GT-100's on the moon. Seeing was fair.

The eyepieces I tested were:
Tele Vue 26mm Plossl - 23x, 2.1° AFOV, Exit Pupil = 4.3mm
Tele Vue 20mm Plossl - 30x, 1.67° AFOV, Exit Pupil = 3.33mm
Takahashi 24mm LE - 25x, 2.08° AFOV, Exit Pupil = 4mm

Some mechanical details:
On my GT-100's eyepieces are a bit easier to insert into the left focuser than into the right. The smooth-sided 26mm plossls insert easier than the newer 20mm plossls which have the channel on the eyepiece barrel. My TAK LE's have smooth-sided barrels, but they were the most difficult to insert. I did not feel very comfortable working the TAK into the left eyepiece holder. Fortunately, the focusers are very solid. Taking out the eyepieces is easier than inserting them. The best method of inserting/removing the eyepieces is to twist the eyepiece opposite the direction of their barrel threads (so that they don't unthread). The friction eyepiece holders are quite snug. I wonder if they will loosen up with more use.

The TV plossls have a much longer focal distance than the TAK LE's. I've noticed this with my PST as well as on the GT-100's. I could bring both types of eyepieces to focus, but the TAK's needed to be adjusted inward quite a bit.

As I stated in my earlier post, the focusers have a lot of fine movement and it was just a little challenging to find the proper focus. The best way on the moon, I discovered, was to focus on a fairly small crater and adjust for sharpness. That worked quite well.

More thoughts on the optics:
All of these eyepieces performed very well with the GT-100's. Unfortunately, I preferred the TAK's over the TV plossls. The TAK's were difficult to insert, but once installed the views were superb. The TAK's seemed a tad sharper, and they are "colder" while the TV plossls are a bit on the "warm" side. Nonetheless, views with each set of eyepieces was quite pleasing. I did not notice much difference in brightness between the 20mm plossls and the others even though the exit pupil was a bit smaller. (I'll need to experiment with some DSO's in this regard.)

On axis views with each set of eyepieces were sharp and displayed a faint green rim around the edge of the moon. The prominence of the CA changed as I adjusted eye position and the placement of the moon in the FOV. Since seeing was only fair, there was probably more CA than can be expected on a better night. Interestingly, if I moved the moon to the right side of the FOV the green ring intensified, and if I moved the moon the the left side of the FOV it turned to purple.

I did not notice any ghosting or other annoying glares.

After experimenting with all this, I inserted the 26mm plossls and spent some time just enjoying the views. The GT-100's have sharp optics, and it was great to sit on my lawn chair and have comfortable eye position. (No sore neck tomorrow.

)

Still very pleased!

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Ed Kessler

sic itur ad astra (Just to look profound!)

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