Moon Age 14 on Sunday 07-06-09 AM

Raymond_Tse

Dear all,

Some features of Moon Age 14 at Oceanu Procellarum taken by TEC140F7 +TV 2x Powermate + TV8mm EP Projection.

Seeing was not very stable and could not support high magnification focusing on 5DII live view screen.

More information can be found at :-
http://www.raymondtse-lawyer.com/astro/moon/moon_age_14/090607am%20-moon-age-11-highlight-yso-TEC+TV2x+TV8+5D2-640x640x72.htm

Raymond Tse

CHYeung

Dear Raymond,

Very good shoot.

Just out of curiosity, why do you use the barlow and the eyepiece together? If I were you, I would use just the eyepiece and extend the projection distance to get the same magnification.

CH Yeung

CHYeung

Dear Raymond,

Very good shoot.

Just out of curiosity, why do you use the barlow and the eyepiece together? If I were you, I would use just the eyepiece and extend the projection distance to get the same magnification.

CH Yeung

Raymond_Tse

Dear CH,

Sometimes things did not work according to logic but just what you had on hand that night.

The set up (Celestron 2 inch to 1.25 adapter with built-in T-male thread) has been previously used by me in 2005 to couple directly with EOS T-ring for EOS camera. The space in-between before the camera was small but I could still insert a TV 8mm possl due to its short top headroom. There was no way to extend the projection tube (except with another T-thread extension tube).  I just followed the previous setup (self-made photo manual) just to save time.

I now have the Borg EP projection tube (M57) system which allows some sort of projection distance but have not tried out this rig. Would try it later in order to reduce the no. of optical glass and surfaces to enhance contrast.

This single image was quite blurred and not sharply focused. No help even when I tried to stack 8-10 images in Registax5 or Image Plus.

I could blame the cause for blur image due to too many glasses in the optical train.

Raymond Tse

orion

Dear Raymond,

The image was not bad at all with single frame.
The image blur was probably not due to your complex optical train. From your information, the blurring may be due to:
1. too high magnification under normal seeing
2. ISO too low and exposure too long, try to raise ISO to 400 to reduce exposure time
3. mirror mechanism of your camera may be another cause, if possible use mirror lock to raise up the mirror before exposure
4. use continuous mode to record your image in order to get a better image out of a series of images
5. the altitude of the moon was too know to make high magnification image
6. use either barlow or eyepiece for projection

Hope these suggestions may help

mca

Dear Raymond,

It seems the bottleneck lies in the 8 mm Plossol. While eyepiece projection is good to image planets, it is more demanding for the Moon which requires a “flat” field with “even” illumination up to the frame corners. Since you have said the eyepiece was inevitably close to the camera, I doubt such setup did not meet the “flat” field and “even” illumination criteria. You probably note there are darkened corners in your posted image.

Normally I do not use Barlow + eyepiece projection at the same time. If I use eyepiece projection (for planets), I avoid placing the eyepiece too close to the camera.

On the same night, I also imaged the lunar feature called Herigonius dome. It was not the good time to observe Herigonius dome because the lunar terminator was too far away from the feature and the Moon’s altitude was a bit low (~ 40 degrees even at transit). Anyway here is the image, result marginally acceptable and 1/3 FOV was inevitably blocked due to my “better-than-none” site environment (City One Shatin home roof).



Sometimes things did not work as wished but just what you had on hand that night.

AC

Raymond_Tse

"it is more demanding for the Moon which requires a “flat” field with “even” illumination up to the frame corners. Since you have said the eyepiece was inevitably close to the camera, I doubt such setup did not meet the “flat” field and “even” illumination criteria. You probably note there are darkened corners in your posted image."

Alan,
You correctly  predicted the large 4 dark corners which I have cut off. Next time I would place the camera further away from the eyepiece.

Even Powermate 4x cannot  allow me to make high magnification on DSLR camera. That is why I have to use eyepiece projection but cannot find the right type of flat-field eyepiece for my TEC140F7 (which by its own design has certain field curvature of about 11% before field flattner is placed).

Dear Alan and Orion,
Any suggestion of a better eyepiece for flat field projection ?

Raymond

CHYeung

Hi Raymond,

For high magnification eyepiece projection, field curvature of the objective may not be a big issue as only  a vsmall central portion of the image plane is magnified and projected. The field flatness of the eyepiece may be more important.

Takahashi and Pentax used to produce series of projection eyepieces but I don't know whether they are still manufactured. They are also rare in the second hand market. I have read about someone using 8mm movie projector lenses and microfilm reader lenses, these lenses have good field flatness and short focal length that is suitable for projection imaging.  Perhaps, video lenses for CCTV or even webcam may be used in the reverse direction for projection but I have never tried them.

CH

CH Yeung

mca

Dear Raymond,

If your TEC-140 refractor already have had a "curved" field, then a true flat field eyepiece is not the solution. What you need is an optical device that has an "opposite" curvature to offset the TEC defects. It is hard to tell specifically what is this optical device, since we do not know the magnitude and orientation of the curvature (positively or negatively curved, and by how much?). The best way is by "try and error" until you feel comfortable with the trial.

I recall that years ago before film technology declined, Pentax produced the "XP" series flat-field projection eyepiece. This, of course, assumed the preceding optics before XP is ideal. I still got a sample XP (3.8 mm), but I think it is not suitable for a trial with TEC now.

My preference is to use the Powermate Barlow instead of an eyepiece. Powermate has wider lens aperture than the typical short focal length eyepiece, hence less risk of curved field and dark frame corners. If 4X Barlow is not enough, you can cascade like 3X + 2X for 6X, or add an extension tube between Barlow & CCD. I sometimes do this way. However, there are always two limitations：

1.  Seeing --- You may get even worse result if seeing is not supportive.

2.  Nyquist sampling theory --- It says that the optimum sampling is obtained when a lunar feature of angular size equal to your telescope resolution (~0.8 arcsecond for TEC-140) just covers 2 pixels of your CCD. So be careful that the EFL (effective focal length) of your telescope is controlled below a value in order to fit Nyquist. By my experience,  EFL = f/30 is probably approaching the Nyquist threshold, assuming best seeing. Perhaps you could use f/35 at most. At less favorable seeing, EFL better kept below f/20 ~f/30. I am not sure the size of one pixel in Canon 5D, so no exact mathematics can tell now. Best is experiment on your own.

My 2 cents. Please take above as reference only, as one's medicine could turn out to be another man's poison.

AC

[ 本帖最後由 mca 於 2009-6-11 23:18 編輯 ]

ericng

Dear Raymond,

Is your 5D mark II? You may consider to use the HD movie mode to continuously record the raw images, The stacked results can be very stunning.

Use the shortest focus length eyepiece you have and extend the projection distance will be good solution to obtain high magnification. But certainly appropriate sampling is important to balance the size of the features and the magnification limit of your optical system.

Best Regards,

Eric