Comparo - light grasp of 6" f/5 vs. 8" f/4

I recently purchased a Hardin Optical 8" f/4 Newtonian OTA for wide
field visual use and astrophotography. Tonight I compared its light
grasp to the 6" f/5 Celestron SP-C6 OTA I have owned for several years.
You can view the photographic results as tested on M42 and M45 on the
page below. The images are unprocessed (other than the camera's
compression to JPG format).

http://www.geocities.com/smalldob/68duel/

In both cases the camera was a Kodak DC4800 coupled afocally to a 32mm
TeleVue Plossl. The exposure was 16 seconds with the camera set at ISO
400 and f/2.8. The image scales are similar since the focal lengths of
the 6" and 8" are approx. 30" and 32", respectively. I was a little
surprised at how much more nebulosity is visible in M42.

I also gathered a number of uncompressed 9Mb TIF files of M42 and plan
to try to stack and get a little experience processing those to see if
I can bring out any additional detail in the nebula.

Mark

On 10 Feb 2005 20:21:10 -0800, Mark wrote:

I was a little surprised at how much more nebulosity is visible in M42.


I believe the 8" mirror has about twice the surface area of the 6" mirror.
The results would seem to confirm that, IMHO.




--
Martin R. Howell
"Photographs From the Universe of Amateur Astronomy"
http://members.isp.com/universeofama...nomy%40isp.com

Martin R. Howell wrote:
On 10 Feb 2005 20:21:10 -0800, Mark wrote:

I was a little surprised at how much more nebulosity is visible in M42.


I believe the 8" mirror has about twice the surface area of the 6" mirror.
The results would seem to confirm that, IMHO.


I noticed that that 6" has some trailing.. how much would this effect
the contrast of M42? Not suggesting this is significant, only curious.

-tom

Yeah, these were unguided on my CG-5. All I can say is that I did not
change the mount between scopes so there was no intentional bias one
way or the other. I intend to take some more shots with the 8" from a
dark site tonight (LM about 6 instead of 4.5-ish) so that may prove
interesting also.

Mark



vic20owner wrote:
Martin R. Howell wrote:
On 10 Feb 2005 20:21:10 -0800, Mark wrote:

I was a little surprised at how much more nebulosity is visible
in M42.


I believe the 8" mirror has about twice the surface area of the 6"
mirror.
The results would seem to confirm that, IMHO.


I noticed that that 6" has some trailing.. how much would this effect

the contrast of M42? Not suggesting this is significant, only
curious.

-tom

"Mark" wrote in message
oups.com...
Yeah, these were unguided on my CG-5. All I can say is that I did not
change the mount between scopes so there was no intentional bias one
way or the other. I intend to take some more shots with the 8" from a
dark site tonight (LM about 6 instead of 4.5-ish) so that may prove
interesting also.

Mark


Looks like we'll have to wait for your bandwidth quota to be renewed.

)

Sorry about that... I guess you get what you pay for, it usually takes
an hour or so to free up again after the quota has been exceeded.


Ed T wrote:
"Mark" wrote in message
oups.com...
Yeah, these were unguided on my CG-5. All I can say is that I did
not
change the mount between scopes so there was no intentional bias
one
way or the other. I intend to take some more shots with the 8"
from a
dark site tonight (LM about 6 instead of 4.5-ish) so that may prove
interesting also.

Mark


Looks like we'll have to wait for your bandwidth quota to be renewed.

)

Well done! I really appreciate it when people do this kind of work.

Do I detect nebulosity in M45 on the 8"?

On M42, I get slightly better views out of a 6" with my eyes in my
suburban So. Cal neighborhood on a moonless night, closer actually to
the 8" shot, but not as vivid. So I'm a little surprised by the
results.

It would be great to work toward getting the images to where one would
see them in the eyepiece, under given conditions and location.

Matt

Mark, a nice way to make the comparison... could there have been
transparency variations between the shots?

OTOH, given that the 8" has almost double the light grasp of the 6", the
results may be what we should have expected!

How did/do the views compare visually?

The Kodaks (I own a DX3900) also can do some great constellation shots
right off a tripod sans scope. The color saturation of the Kodak
digicam (at least the old ones) was quite remarkable at capturing the
spectral coloring of stars.

Larry Stedman
Vestal

Thanks Larry, I don't think the transparency varied much last night, it
was very clear with a cold front having just cleared us during the day.


I have also done some constellation shots with my Kodak and I agree
they are quite good for this.

Now if I could just learn to coax a little more deep sky detail out of
the ether with Registax I would be happy!

Mark


Larry Stedman wrote:
Mark, a nice way to make the comparison... could there have been
transparency variations between the shots?

OTOH, given that the 8" has almost double the light grasp of the 6",
the
results may be what we should have expected!

How did/do the views compare visually?

The Kodaks (I own a DX3900) also can do some great constellation
shots
right off a tripod sans scope. The color saturation of the Kodak
digicam (at least the old ones) was quite remarkable at capturing the

spectral coloring of stars.

Larry Stedman
Vestal

As a rule of thumb, to double light gathering ability, a mirror needs to be
approx 1.4 times the size of the first mirror. To reduce it by half, the
mirror should be .7 times as large. It's useful when you start thinking how
much bigger do I need to go...

;-)

Chuck Taylor
Do you observe the moon?
Try http://groups.yahoo.com/group/lunar-observing/

Are you interested in understanding optics?
Try http://groups.yahoo.com/group/ATM_Optics_Software/

************************************

"Martin R. Howell" wrote in message
...
On 10 Feb 2005 20:21:10 -0800, Mark wrote:

I was a little surprised at how much more nebulosity is visible in M42.


I believe the 8" mirror has about twice the surface area of the 6" mirror.
The results would seem to confirm that, IMHO.




--
Martin R. Howell
"Photographs From the Universe of Amateur Astronomy"
http://members.isp.com/universeofama...nomy%40isp.com