Re: [M]: Field De-rotators
| Subject: | Re: [M]: Field De-rotators |
| From: | Doc Gs binc mail address |
| Date: | Sat Mar 01 13:15:40 1997 |
At 08:40 AM 3/1/97 -0800, you wrote:
>Hi Guys,
>
>Thought I should chime in on the derotator discussion:
>
>I have been reading the MAPUG notes on the subject and look forward to the
>introduction of such an accessory. The 16" LX200 already has one and I
suppose it was
>a matter of time before they were introduced for the 8"-12" LX200s. I hope
the price
>is right. Assuming it works as intended, it would be a good accessory to
have in the
>arsenal. Although useful, field de-rotation does not make polar alignment
obsolete in
>all cases.
>
>Here are some advantages and limitations that I see.
>
>Advantages:
>
>1. There is no question that a fork mounted LX200 is mechanically more
stable in
>ALT-AZ mode than in Polar (especially for low lat observers). The ALT-AZ
>configuration is very rigid.
>
>2. Computer aided alingment is easier in ALT-AZ mode.
>
>3. There is one less piece of fairly heavy hardware to haul around.
>
>Limitations:
>
>1. Field derotation will only help the primary optics. Forget piggy-back
photography
>and separate guide scopes. You still need polar mode for that stuff.
>
>2. Depending on the physical size of the de-rotator, there may be problems
with rear
>cell accessories like CCD cameras clearing drive base when pointing over head.
>
>3. Even if you are not looking overhead, is the LX200 smart enough to
never slew the
>rear cell between the forks when moving to a new object? I dont know. If
it is not
>and your accessory package extends too far...KLANK. After your heart
starts again you
>will be scrambling to do an emergency shut down and praying nothing is damaged!
>
>I guess my recommendation is that it (a de-rotator) will be a useful
accessory in many
>instances but cannot totally replace an equatorial alignment in the LX200s
case. So
>guys and gals, dont throw your wedges away just yet!
>
>Ken Milburn
>Hi Guys,
>
>Thought I should chime in on the derotator discussion:
>
>I have been reading the MAPUG notes on the subject and look forward to the
>introduction of such an accessory. The 16" LX200 already has one and I
suppose it was
>a matter of time before they were introduced for the 8"-12" LX200s. I hope
the price
>is right. Assuming it works as intended, it would be a good accessory to
have in the
>arsenal. Although useful, field de-rotation does not make polar alignment
obsolete in
>all cases.
>
>Here are some advantages and limitations that I see.
>
>Advantages:
>
>1. There is no question that a fork mounted LX200 is mechanically more
stable in
>ALT-AZ mode than in Polar (especially for low lat observers). The ALT-AZ
>configuration is very rigid.
>
>2. Computer aided alingment is easier in ALT-AZ mode.
>
>3. There is one less piece of fairly heavy hardware to haul around.
>
>Limitations:
>
>1. Field derotation will only help the primary optics. Forget piggy-back
photography
>and separate guide scopes. You still need polar mode for that stuff.
>
>2. Depending on the physical size of the de-rotator, there may be problems
with rear
>cell accessories like CCD cameras clearing drive base when pointing over head.
>
>3. Even if you are not looking overhead, is the LX200 smart enough to
never slew the
>rear cell between the forks when moving to a new object? I dont know. If
it is not
>and your accessory package extends too far...KLANK. After your heart
starts again you
>will be scrambling to do an emergency shut down and praying nothing is damaged!
>
>I guess my recommendation is that it (a de-rotator) will be a useful
accessory in many
>instances but cannot totally replace an equatorial alignment in the LX200s
case. So
>guys and gals, dont throw your wedges away just yet!
>
>Ken Milburn
In addition to these very valid remarks, note that there is no real evidence
that such derotators are actually headed for the market. So far only rumors
on MAPUG. Also, the best photography or imaging is at or near zenith due to
sky polution. The alt/asm setup has great difficulties working at the
zenith. Also, the derotator does not work well in a rather large cone of
view where the scope has to move quickly or the derotator has to rotate
quickly to keep alignment. I second the thought of keeping that wedge.
Doc G
>
