the Meade Pictor 201XT
problems and solutions


Here is really a debated object: this is the lightest, simplest and most cheap CCD autoguider on the market, but in some cases it is not very efficient and many people consider it just an useless toy.
In my experience,on the contrary, I have found that it can work with good results: you just have to find a workaround to its main faults.


  1. check your off-axis guider
  2. focusing the telescope
  3. search for the best guide star
  4. set the correct Exposure Time for the CCD
  5. focusing the autoguider
  6. calibration
  7. Pictor 201XT Mode Diagram

Note: this is not a complete course about the 201XT, I just describe my solutions for the most important problems: I assume that you already know the 201XT Users Guide for the general setup. Other tips about this autoguider are available in the MAPUG Topical Archive.


1. check your off-axis guider (OAG)

I do not want to cause a controversial, but in my opinion with a Schmidt-Cassegrain telescope it is not possible to use a guidescope for long exposures: the mirror slop will cancel the guiding accuracy. I wasted a lot of time this way.
Now I use an Off-Axis Guider: it is more difficult to find a good star, but the OAG uses the same objective that makes the photo and compensates for possible slops.
Check your OAG and measure the difference between the optical axis and the centre of the OAG eyepiece's field of view. For example in the Meade OAG I have found a difference of about 45 arc minutes.
A direct look in the camera and in the eyepiece is probably the easiest way to get this measure. It will be useful for chosing a correct guide star.


2. focusing the telescope for the photography

I describe my methods in another page.
Anyway you must not change this position when you will focus the CCD.


3. search for the best guide star

The Pictor 201XT works better with guide stars between mag.4 and mag.8. It is not cooled: for this reason you cannot use very faint stars and for better results you always have to look for the brightest star that is possible.
I study the situation on a sky atlas: I use Megastar 3, but suppose that other programs are good as much.
Look at the chart below: it is an example for a photo of NGC 7635

The green rectangle is the field of the 35mm camera; the blue circle is the center of the OAG eyepiece field of view rotated around the optical axis (in this example for the Meade OAG: as I said its radius is 45').
You have to find a good star on this circle, if possible by letting the nebula in the center of the field. Actually it should be on the inferior semicircle: since the telescope gives inverse images this way the guiding port will stay up (it is very difficult to look in an eyepiece directed below!). Note that for the same reason the real position of the guiding port will always be opposite to the position of the star in the chart.
This chart shows an ideal situation with a good guide star (mag.6.9) in the perfect position to let the Bubble Nebula in the center of the image. Other cases are less lucky, but almost everytime I can find a satisfactory configuration...really some objects are very difficult (or quite impossible!).
Usually I work on the configuration in the days before and print a chart to be used near the telescope: with a "mirror" chart you will have the exact field as seen in the OAG eyepiece.
Be sure to avoid double stars (apparent double too...) with a bright companion within a 1 arc minute radius and remember that star catalogues contain a lot of errors: when you will have found a good star check it with another catalogue!

Now you are ready to start: center the object in the camera field and look for the guide star you chose rotating the OAG and moving (not much!) the telescope until it is centered, first in a wide field eyepiece then in a hight power reticle.
Now you have to chose the correct Et.


4. set the correct Exposure time for the CCD

The Pictor 201XT has a range of Exposure times (Et) from 0.1 to 25 seconds. Of course a shorter time gives a better result, cause it means more frequent corrections; only in rare cases a quite long Et could minimize the harmful influence of a very bad seeing (in these cases is probably better to stay at home and look at TV...).

The relationship between Et and the star mag. (for brightness values of about 20) is described in the diagram on the right. It is obtained by a LX200 8" f:6.3 and the Meade OAG.
It is rule-of-thumb at all, founded on my experience and probably not very correct, but it can give you an idea of the initial Et for starting setup. Usually I find that this is also the right time for guiding the photo.


5. focusing the autoguider

You have already focused the photocamera. Now do not use the focus knob of the telescope: for focusing the Pictor move it up and down in the OAG eyepiece holder.
I have studied the criticality of the focus accuracy and show it in this diagram: I moved the focus by 2/10mm steps reading the corresponding brightness value (actually it is the average of five readings).
The diagram says which precision is required and you can make an accurate job only adding a graduated scale to the Pictor's barrel as shown in the picture. In my opinion 0.75mm steps are a good compromise between precision and concrete realization.

I simply used a strip of paper (drawn and printed by the pc) rolled up to the barrel; you can see the section below: the height is 12 mm and the width 99 mm.

Move the Pictor of one step (control the position with the edge of the eyepiece holder) and read the brightness values until you get the maximum.
Increase then Et if you do not have at least a value of 15-20 in the perfect focus.


6. calibration

The 201XT works better if the CCD is parallel to RA and dec. circles: this way you minimize the bad influence of dec. axis backlash and it is easier to center the guide star with the slow motions of the telescope.
As described by M.Hart in the Mapug topical archive you can get this result rotating the autoguider in the same number of degrees and direction as you rotated the OAG eyepiece around the optical axis.

Now we have a problem: with the Meade OAG it is not possible to rotate the Pictor more than 50° because it touchs the telescope. The solution is turn the autoguider of the inverse of the complementary angle.
For example: if you have rotated the OAG of 75° clockwise, turn the 201XT of 90°-75°=15° anticlockwise: the CCD chip will be parallel to the reversed axis. Reading the position of the guide star on the display the first digit will show the dec. and the second digit the RA.
I recalibrate every time, because I cannot be sure to insert the autoguider exactly in the same position of the last time.
A tip: if your telescope obstinately refuse to calibrate and shows Error in the display try to turn the Pictor of few degrees.


7. Pictor 201XT Mode Diagram

I redrew the User guide's mode diagram for using near the telescope.

Good luck
Do not hesitate to contact me if you still have problems!


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