iStar 127 F/5.5 Build from Oz

[GrahamP]

Hey all,
I picked up a second hand iStar D127 F5.5 objective last week and couldn't resist making a quick and dirty setup so I could try it out.
Ales informs me that these short F ratio achromats are good to about 0.25 x Lens Diameter = 32x for this one. That means the potential for a light and highly portable star gazer is at hand. I'm all for that!



I have bolted up some aluminium tube and angle with a rubbish focuser (Bushmaster F500) which makes it work.



So I tried this last night (with no moon visible, but some sky glow and scattered clouds). Didn't get to view anything of particular interest due to cloud and telescope position, but can compare results for the M35 open cluster.

• 24mm Televue Panoptic, 29x  Lovely crisp star images right across the field. Nice.
• 18mm Televue Radian, 39x Also very nice.
• 13mm Televue Nagler T6, 54x Good view that I would consider a practical limit on the night.
• 9mm Vixen NLV, 78x, Star images starting to break down a bit and lose their appeal.

I could agree that around 32x might be ideal for this lens, but I would be happy at 54x.
I will add some more observations when I have used it some more.

cheers .... Graham.P

[nobody]

Hi Graham,

Congratulations on your build. I like the use of square tubing to provide a backbone.

Have you made any progress since your last post?

Too obvious to mention, but you might get better contrast if you blacken inside the focuser area and add a baffle or two.

A Fringe Killer filter might also be useful.

Stay safe,
Chris

[GrahamP]

Thanks Chris,

it's a minimalist design for sure, just enough to let me try it out. It weighs 4.4Kg (9.75lb), so is heavier than my intended build which will be sheet metal, closed with baffles, similar to my other project here:-

istarscopeclub.proboards.com/thread/723/istar-180-r30-build-oz

I have found that it is fun to use, and I have used it 5 times now. I have found I can go higher with magnification, depending on seeing and on the target. With M42 100x is comfortable with a TV7N1. The 4 trapezium stars are nice and sharp.

The Jewel Box (NGC4755) was lovely with my TV 24mm Panoptic or up to TV 6mm Radian, very good.

Omega Centauri was nearly overhead at midnight and a magnificent view, breaking down to individual stars with a TV 13mm Nagler T6. On this night, temperature was 9°C with no wind and very little star twinkle.

The long smudge of edge on barred spiral NGC4945 was easily seen, as were 10 or so globular clusters around the Southern Cross and the tail of Scorpio including NGC6541, NGC6397 & NGC6752 (notable with individual stars popping out).

I also compared its performance with a Takahashi TSA-102 and Skywatcher ED120 which are a tad sharper than the iStar at higher magnifications (say 50x to 100x), but the iStar performs wonderfully for what it is, and is fun and rewarding to use on many deep sky objects.

Regards... Graham