Depends on where you place the acrylic. If before the negative no change in focus. If after the negative, i.e. the negative resting on the acrylic them you will alter the distance from the negative to the lens and you will need to refocus. If after the lens - no change. If you are putting before or after the negative make sure it is clean and dust free - else they will be enlarged as well. Hope this helps Mike -----Original Message----- From: pure-silver-bounce@xxxxxxxxxxxxx [mailto:pure-silver-bounce@xxxxxxxxxxxxx] On Behalf Of Peter De Smidt Sent: Friday, February 29, 2008 5:00 PM To: pure-silver@xxxxxxxxxxxxx Subject: [pure-silver] Optical question Suppose one were to put a piece of 5mm thick acrylic between a negative and an enlarging lens. Would the piece of acrylic cause the distance needed to focus the negative at a given size to change? If so, would there need to be more or less extension between the negative and the lens? ============================================================================ ================================= To unsubscribe from this list, go to www.freelists.org and logon to your account (the same e-mail address and password you set-up when you subscribed,) and unsubscribe from there. ============================================================================================================= To unsubscribe from this list, go to www.freelists.org and logon to your account (the same e-mail address and password you set-up when you subscribed,) and unsubscribe from there.