How does Istar compare to???

[astrosean]

I spent an hour tonight looking through a Jaeger's 6" f15 objective I purchased from Surplus Shed. This objective is from the last of Jaeger's stock and is a throw back to the old days of long refractors.

I have to say the images left a bit to be desired. Compared to my IStar, they did not quite measure up. Because the Jaeger's objectives are uncoated, the images were noticeably dimmer. The star test was very good and stars were pin-points however there were odd reflections when I moved my eye off axis, most likely a result of the lack of coating on the objective.

I am waiting for Jupiter to rise before making a final determination but for now my Istar is safe and secure...

In the back of my mind I have always had the opinion that "glass is glass" however the more experience I get looking through other scopes the more I feel I was fortuitous in my choice of Istar objective!

[Ales - iStar Optical]

Sean, I am more than happy to see your post on direct comparison between Istar and Jaegers achromatic doublet. Comments like these help our credibility. There are still many undecided buyers and your post should help these guys in making the right decission and go for a brand new Istar objective lens. Keep us informed!
cheers,
Ales
Istar Optical, owner

[Watcher3]

Hey Sean. How did you make out with the ronchi testing on the Jaegers?

[astrosean]

I bought both a 4" f15 an a 6" f15. Both lenses tested very well. I was very surprised to find sharp black stripes for both with no curves or edge-issues. I haven't set up a double-pass setup, that is a bit complicated, I need a large flat and a large ronchi screen. My ronchi eyepiece is good for errors to about 1 wave so I relied on a star test for the ultimate word. I have not star tested the 4" as I don't have a way to mount it just yet.

I went out very late last night and checked out Jupiter... The Jaeger's lack of coatings really made the experience a chore. The view wasn't so bad on-axis but as soon as I lost eye placement the flares, ghosts and haze erupted. To the objective's credit, jupiter was very sharp but the lack of coatings and uncontrolled reflections muted the detail. It was like looking through a dew-covered objective. In comparison the Istar offers extreme contrast and APO like clarity, no contest.

Now I am trying to figure out what to do with the thing. I could send it out for AR coatings for $125 or try to sell it for what I paid for it(maybe less).


Sean

[Watcher3]

Good to hear that they are figured well, as I got a 4" F/15 as well. The one report of a bad Jaegers on CN had me a little worried, as I have no means to test mine until I'm getting ready to build it. A long time from now, as I recover from my ISTAR 6" upgrade path! Started out ordering a 6" F/5 achro, and in a very confused cycle of self doubting incremental steps ended up with a complete R60 OTA with Feathertouch focuser!

If the Jaegers F/15 can hold a candle to my 100/1300 Carton, I'll build it into a showpiece OTA for a future permanent mount. Of course it won't get a lot of use after I get a 180 lanthanum super apo!

If I were you, I would have the Jaegers coated. Even if it still doesn't surpass the ISTAR, you can put it away until the Jaegers lenses get scarce. Then you'd have a known good example of a "collector" lens to sell if you want.

[Watcher3]

Forgot to ask. What did you use fora cell?

[mikey cee]

Sean....Are you absolutely positive that those reflections are due to lack of coatings or is it the cell? Are you using the same cell and tube also? The eyepiece is probably the same used with the Istar. The reason I ask is because my Brandt 8" f/13.3 is also uncoated but I get crisp and contrasty views of Jupiter and Saturn just like my coated Jaegers 6" f/8 with no hint of ghost or reflections. ???Mike

[bluestar]

I agree with Mikey...lack of coatings would not cause the abberations yo see. There is something funky going on with that glass from 'Surplus and I wouldn't consider this a credible comparo with the Jaegers name.

[gord]

Based on my experience with coatings, I'd agree with Sean that lack-of will cause the problems he seen. Two somewhat recent experiences with this come to mind:

1. the early proto-type 160LaF lens that I tested this spring had a noticeable lack of coatings as compared to my 150F10. This was also noted by others in the pictures I posted of the lens. In testing, I just couldn't get clear of ghost images and lightness in the field, and it was very sensitive to eye placement.

2. Brandon eyepieces. I know lots of people like them, but I can't get past the lack of coatings. Not only does it make them very dim compared to anything else, but they are especially terrible for solar work. The reflections back off of the eyeball just completely wash out the field and introduce noticeable ghosts and haze. I had really hoped they would be good for solar, but that is where I found they were the overall weakest.

So, I find coatings to be an absolute must. From reading some old refractor design books, it is somewhat dependant on the design as well. Some were specifically noted as being good options for un-coated since the spacing and radius of curves would avoid these problems. Oil spaced would be another case where it wouldn't matter.

Clear skies,
-Gord

[Mike]

Gord, I know it's off subject but what kind of solar viewing you like? White light or Ha? Imaging?

Mike