This allows viewing and photographing the same object simultaneously. This is easy to do since the T threads on the guider fit most eyepiece-projection systems used for planetary imaging. The actual exposures should be made with the mirror retracted to eliminate diffraction effects and light loss in the image. Despite the many adjustments that are possible with the SpectraGuide, the unit proved to be very rigid. One of four tests done with the ST-4 CCD autotracker did show signs of flexure, so anyone using such an arrangement should be especially careful to tighten the various thumbscrews and secure the cable leading from the CCD head.
Many photographers like to boost the magnification of a guiding eyepiece with a Barlow lens.
It's almost impossible to imagine, let alone test, all the combinations possible with these off-axis guiders and the various Barlows sold today. But of the several I put together from my own collection of equipment, some would come to focus and some would not. Unfortunately, there's no simple way to predict whether a particular system will work. Knowledgeable dealers may be able to advise you regarding specific combinations. One thing is certain about both of these guiders.