LIVE CHAT with Michael Barber from SBIG

[BT Technologies]

A new page entry has been added:

[drupal=24]LIVE CHAT with Michael Barber from SBIG[/drupal]

We are proud to announce that Michael Barber from SBIG (Santa Barbara Instrument Group) will be hosting a LIVE CHAT right here on Astroclassifieds.com

<font size="2">Mike will be available to answer your questions about SBIG

[pytom]

I have only one question. Why is the STV no longer available, i.e., I own one and wonder why SBIG no longer makes this fine product. Tom Mote

[BT Technologies]

Hello Tom,

You can ask this question to Michael on our SBIG Live Chat on 06/27/07 @ 9:30 PM!!

I would like to know the answer to this question as well...

[raf1]

Hi Brian - had to work late tonight and missed the chat. Will a transcript be made available?

Thanks.

Ron

[BT Technologies]

Hello Ron,

I will see what I can do to grab the entire transcript and post it here. We had a server issue 40 minutes into the chat so I should have everything up to that point.

[jonesmi]

Would like to discuss Takahashi focus shifts with temperature and see what they know, or if there are a thermal models. I have measured focus shifts on my TOA-130S of about 0.0005" to 0.001" per degree F., with the focus moving toward the lens as temperatures fall.

Would also at least like to see a cross section drawing of the TOA lens. Those must be some thick chunks of glass in there.

Mike

[suburbanskies]

Originally Posted by jonesmi

Would like to discuss Takahashi focus shifts with temperature and see what they know, or if there are a thermal models. I have measured focus shifts on my TOA-130S of about 0.0005" to 0.001" per degree F., with the focus moving toward the lens as temperatures fall.

Would also at least like to see a cross section drawing of the TOA lens. Those must be some thick chunks of glass in there.

Mike

Yeah, Mike I'd love to see a cross section of the TOA-130, too. Not that I could make much sense of it, but that kind of stuff is cool!

Somehow, the French Takahashi dealer seems to get a lot of tech details. Wish that the same was available here in the US.

Mark

[Bryan_Tiffany]

"...I have measured focus shifts on my TOA-130S of about 0.0005" to 0.001" per degree F., with the focus moving toward the lens as temperatures fall..."


Hello Mike,

I suspect what you're seeing is the thermal contraction of the aluminum tube. A commonly used aluminum, like 6061-T6, has a thermal coefficient of expansion (CTE) of 13.5x10-6 inches, per inch of length and per degree F. The length of the tube is roughly the same as the focal length (1000mm = 39.4"), so the TOA-130 tube will shrink (or grow) about 0.0005" for every 1 degree F change in temperature.

The lenses in the objective will also change shape slightly with termperature (depending on their CTEs), resulting in a change in the effective focal length, but I suspect this effect will be less pronounced than the change in tube length. You would need a detailed prescription of the lens (radii, center thicknesses, and materials) to accurately assess the objective's contribution.

These days, many astrograph designs are using carbon-fiber tubes (CTE typically 1/10th that of aluminum) as the tube, rather than aluminum, to help mitigate this effect. The CTE of carbon-fiber can be tailored to the application and can even have a negative CTE (material grows with decreasing temperature). It can also have different CTEs in different directions (axial versus diametral). The Hubble Telescope's metering structure is made of carbon-fiber.

Bryan Tiffany