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Hello. I would like to know if anyone who has changed the focuser on this Newton has had focusing problems. In my case, when changing from an SV200 filter to an Lpro filter, I cannot focus for 150 focuser steps. The focusing shaft is fully inserted and stops. Am I doing something wrong?  |
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Try to reduce at 30 steps.
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Iosif Bodnariu: Hi the problem is not the steps, because when it´s stop the star is unfocused. So i need a couple of milimeters to get focus |
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If you are hitting the bottom of the focuser's range the only thig you can do is move the focal plane out by moving the primary closer to the secondary by a small amount or remove or change something in your imaging train so you can reduce the distance from the top of the focuser body to the sensor. If you are really close can also try moving the primary closer just by adjusting the collimation bolts the same amount inward. Newts are very flexible this way so don't be afraid to make changes if you need to.
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Tony Gondola: Thanks. Great idea |
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If you are going to use a coma correct as you probably would the said corrector would push the focus out, sometimes considerably, depending on the specific of the coma corrector. The widely regarded SW 4-elements one will push it out by 20mm.
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I'm also looking for a replacement for the stock Crayford focuser for my 150PDS, but all I found was for 8" and up. Even the customer support of a shop here in Germany was not 100% sure which focuser would fit the Skywatcher 6" to be able to get into focus. That's why I had given up the search again. At least in this case, cyck says it would fit. And they also took a picture of it as a product image. ;-) I keep my fingers crossed that you find a solution. For the price it looks quite sturdy and promising. |
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I would be pushing the primary mirror further up the tube using the push screws on the back… That's your easiest option to get a 'few millimeters'… If it turns out that a few millimeteres is not enough, you may have to consider something like what I had to do to my 8" F/6 newt back in the day, and cut 1" (~25mm) off the bottom of the OTA, re-drill holes for the primary mirror cell, then re-mounting the cell, re-collimate, then your focus point will be 25mm further out than it was before. Problem solved… As Andrea mentioned though - if you do not yet have a coma corrector in the light path, I would not resort to any drastic action yet, as they can significantly alter the focus point of the telescope. Alex. |
